Buck Boost Transformer Selection Guide

You should have the following information before selecting a buck boost transformer.

Line Voltage - The voltage that you want to buck (decrease) or boost (increase). This can be found by measuring the supply line voltage with a voltmeter.

Load Voltage - The voltage at which your equipment is designed to operate. This is listed on the nameplate of the load equipment.

Load KVA or Load Amps - You do not need to know both - one or the other is sufficient for selection purposes. This information usually can be found on the nameplate of the equipment that you want to operate.

Frequency - The supply line frequency must be the same as the frequency of the equipment to be operated - either 50 or 60 cycles.

Phase - The supply line should be the same as the equipment to be operated - either single or three phase.

4 Step Selection

1) From the top row of the chart, find the high and low voltage combination that is closest to the one you require.

2) Move down that column to the kVA or Ampere rating equal to or greater than the rating required by the load.

3) From the far left column, obtain the transformer catalog model.

4) The corresponding connection diagram is indicated at the top of each Voltage/kVA column. Click on the link view the diagram.

Index

1 Phase Buck Boost Transformers
3 Phase Buck Boost Transformers

FAQ

Product Selection - 1 Phase Buck Boosts

Group 1 - 120x240 Input, 12/24 Output

	Models by Brand	Line Voltage	96	100	100	105	110	110	115	115	120	120	200	208	220	220	240	240
	Models by Brand	Load Voltage	115	110	120	115	121	132	126	138	132	144	220	229	231	242	252	264
Connection Diagram			2	1	2	1	1	2	1	2	1	2	4	4	3	4	3	4
1	Federal	HV Amps	2.08	4.17	2.08	4.17	4.17	2.08	4.17	2.08	4.17	2.08	2.08	2.08	4.17	2.08	4.17	2.08
		kVA	0.24	0.46	0.25	0.48	0.504	0.28	0.53	0.29	0.55	0.3	0.49	0.48	0.96	0.504	1.05	0.55
		LV Amps	2.5	4.58	2.5	4.58	4.58	2.5	4.58	2.5	4.58	2.5	2.29	2.29	4.38	2.29	4.38	2.29
2	Federal	HV Amps	4.17	8.33	4.17	8.33	8.33	4.17	8.33	4.17	8.33	4.17	4.17	4.17	8.33	4.17	8.33	4.17
		kVA	0.48	0.91	0.5	0.961	1.01	0.55	1.05	0.57	1.1	0.6	0.917	0.953	1.92	1.01	2.1	1.1
		LV Amps	5	9.17	5	9.17	9.17	5	9.17	5	9.17	5	4.58	4.58	8.75	4.58	8.75	4.58
3	Federal	HV Amps	6.25	12.5	6.25	12.5	12.5	6.25	12.5	6.25	12.5	6.25	6.25	6.25	12.5	6.25	12.5	6.25
		kVA	0.72	1.38	0.75	1.44	1.51	0.825	1.58	0.83	1.65	0.9	1.38	1.43	2.88	1.51	3.15	1.65
		LV Amps	7.5	13.8	7.5	13.8	13.8	7.5	13.8	7.5	13.8	7.5	6.88	6.88	13.1	6.88	13.1	6.88
4	Federal	HV Amps	10.4	20.8	10.4	20.8	20.8	10.4	20.8	10.4	20.8	10.4	10.4	10.4	20.8	10.4	20.8	10.4
		kVA	1.2	2.29	1.25	2.4	2.52	1.37	2.63	1.44	2.75	1.5	2.29	2.38	4.81	2.52	5.25	2.75
		LV Amps	12.5	22.9	12.5	22.9	22.9	12.5	22.9	12.5	22.9	12.5	11.4	11.4	21.8	11.4	21.8	11.4
5	Federal	HV Amps	20.8	41.6	20.8	41.7	41.7	20.8	41.7	20.8	41.7	20.8	20.8	20.8	41.7	20.8	41.7	20.8
		kVA	2.39	4.58	2.5	4.8	5.04	2.75	5.26	2.87	5.5	3	4.58	4.77	9.62	5.04	10.5	5.5
		LV Amps	24.9	45.8	25	45.8	45.8	25	45.8	25	45.8	25	22.9	22.9	43.7	22.9	43.7	22.9
6	Federal	HV Amps	31.2	62.5	31.2	62.5	62.5	31.2	62.5	31.2	62.5	31.2	31.2	31.2	62.5	31.2	62.5	31.2
		kVA	3.6	6.87	3.75	7.2	7.56	4.12	7.89	4.31	8.25	4.5	6.87	7.15	14.4	7.56	15.7	8.25
		LV Amps	37.5	68.7	37.5	68.7	68.7	37.5	68.7	37.5	68.7	37.5	34.4	34.4	65.6	34.4	65.6	34.4
7	Federal	HV Amps	41.7	83.3	41.7	83.3	83.3	41.7	83.3	41.7	83.3	41.7	41.7	41.7	83.3	41.7	83.3	41.7
		kVA	4.8	9.17	5	9.6	10.1	5.5	10.5	5.75	11	6	9.17	9.53	19.2	10.1	21	11
		LV Amps	50	91.7	50	91.7	91.7	50	91.7	50	91.7	50	45.8	45.8	87.5	45.8	87.5	45.8
8	Federal	HV Amps	62.5	125	62.5	125	125	62.5	125	62.5	125	62.5	62.5	62.5	125	62.5	125	62.5
		kVA	7.2	13.7	7.5	14.4	15.1	8.25	15.8	8.62	16.5	9	13.7	14.3	28.9	15.1	31.5	16.5
		LV Amps	75	137	75	137	137	75	137	75	137	75	68.7	68.8	131	68.7	131	68.7
9	Federal	HV Amps	83.3	166	83.3	166	166	83.3	166	83.3	166	83.3	83.3	83.3	166	83.3	166	83.3
		kVA	9.58	18.3	10	19.2	20.1	11	21	11.5	22	12	18.3	19	38.5	20.1	42	22
		LV Amps	99.8	183	100	183	183	100	183	100	183	100	91.7	91.7	175	91.6	175	91.6
10	Federal	HV Amps	125	250	125	250	250	125	250	125	250	125	125	125	250	125	250	125
		kVA	14.4	27.5	15	28.8	30.2	16.5	31.5	17.2	33	18	27.5	28.6	57.7	30.2	63	33
		LV Amps	150	275	150	275	275	150	275	150	275	150	137	137	262	137	262	137
11	Federal	HV Amps	208	417	208	417	417	208	417	208	417	208	208	208	417	208	417	208
		kVA	24	45.8	25	48	50.4	27.5	52.7	28.7	55	30	45.8	47.7	96.3	50.4	105	55
		LV Amps	250	458	250	458	458	250	458	250	458	250	229	229	438	229	438	229

Group 2 - 120x240 Input, 16/32 Output

	Models by Brand	Line Voltage	95	101	106	110	110	115	115	120	120	203	208	220	220	230	240	240
	Models by Brand	Load Voltage	120	115	120	125	139	130	146	136	152	230	236	235	249	261	256	272
Connection Diagram			2	1	1	1	2	1	2	1	2	4	4	3	4	4	3	4
1	Federal	HV Amps	1.56	3.13	3.13	3.13	1.56	3.13	1.56	3.13	1.56	1.56	1.56	3.13	1.56	1.56	3.13	1.56
		kVA	0.188	0.36	0.38	0.39	0.22	0.41	0.23	0.44	0.24	0.36	0.37	0.73	0.39	0.41	0.8	0.43
		LV Amps	1.98	3.54	3.54	3.54	1.98	3.54	1.98	3.54	1.98	1.77	1.77	3.33	1.77	1.77	3.33	1.77
2	Federal	HV Amps	3.12	6.25	6.25	6.25	3.12	6.25	3.12	6.25	3.12	3.12	3.12	6.25	3.12	3.12	6.25	3.12
		kVA	0.376	0.72	0.75	0.78	0.44	0.82	0.46	0.85	0.48	0.72	0.74	1.47	0.78	0.82	1.6	0.85
		LV Amps	3.96	7.08	7.08	7.08	3.96	7.08	3.96	7.08	3.96	3.54	3.54	6.67	3.54	3.54	6.67	3.54
3	Federal	HV Amps	4.69	9.38	9.38	9.38	4.69	9.38	4.69	9.38	4.69	4.69	4.69	9.38	4.69	4.69	9.38	4.69
		kVA	0.564	1.07	1.13	1.17	0.653	1.22	0.683	1.28	0.713	1.08	1.1	2.2	1.17	1.22	2.4	1.28
		LV Amps	5.94	10.6	10.6	10.6	5.94	10.6	5.94	10.6	5.94	5.31	5.31	10	5.31	5.31	10	5.31
4	Federal	HV Amps	7.81	15.6	15.6	15.6	7.81	15.6	7.81	15.6	7.81	7.81	7.81	15.6	7.81	7.81	15.6	7.81
		kVA	0.94	1.8	1.87	1.95	1.09	2.04	1.14	2.12	1.19	1.8	1.84	3.67	1.95	2.04	4	2.12
		LV Amps	9.9	17.7	17.7	17.7	9.87	17.7	9.9	17.7	9.9	8.85	8.85	16.7	8.85	8.85	16.7	8.85
5	Federal	HV Amps	15.6	31.2	31.2	31.2	15.6	31.2	15.6	31.2	15.6	15.6	15.6	31.2	15.6	15.6	31.2	15.6
		kVA	1.88	3.59	3.75	3.9	2.18	4.07	2.28	4.25	2.37	3.59	3.68	7.33	3.9	4.07	8	4.25
		LV Amps	19.8	35.4	35.4	35.4	19.8	35.4	19.8	35.4	19.8	17.7	17.7	33.3	17.7	17.7	33.3	17.7
6	Federal	HV Amps	23.4	46.8	46.8	46.9	23.4	46.9	23.4	46.9	23.4	23.4	23.4	46.9	23.4	23.4	46.9	23.4
		kVA	2.82	5.39	5.63	5.84	3.27	6.1	3.41	6.37	3.56	5.39	5.53	11	5.84	6.11	12	6.37
		LV Amps	29.7	53.1	53.1	53.1	29.7	53.1	29.7	53.1	29.7	26.6	26.6	50	26.6	26.6	50	26.6
7	Federal	HV Amps	31.2	62.5	62.5	62.5	31.2	62.5	31.2	62.5	31.2	31.2	31.2	62.5	31.2	31.2	62.5	31.2
		kVA	3.76	7.18	7.5	7.79	4.35	8.15	4.55	8.5	4.75	7.19	7.37	14.7	7.79	8.15	16	8.5
		LV Amps	39.6	70.8	70.8	70.8	39.6	70.8	39.6	70.8	39.6	35.4	35.4	66.7	35.4	35.4	66.7	35.4
8	Federal	HV Amps	46.9	93.7	93.7	93.7	46.9	93.7	46.9	93.7	46.9	46.9	46.8	93.7	46.9	46.9	93.7	46.9
		kVA	5.64	10.8	11.2	11.7	6.53	12.2	6.83	12.7	7.12	10.8	11	22	11.7	12.2	24	12.7
		LV Amps	59.4	106	106	106	59.4	106	59.4	106	59.4	53.1	53.1	100	53.1	53.1	100	53.1
9	Federal	HV Amps	62.5	125	125	125	62.5	125	62.5	125	62.5	62.5	62.5	125	62.5	62.5	125	62.5
		kVA	7.5	14.4	15	15.6	8.71	16.3	9.1	17	9.5	14.4	14.7	29.3	15.6	16.3	32	17
		LV Amps	79.1	142	142	142	79.2	142	79.2	142	79.2	70.8	70.8	133	70.8	70.8	133	70.8
10	Federal	HV Amps	93.7	187	187	187	93.7	187	93.7	187	93.7	93.7	93.7	187	93.7	93.7	187	93.7
		kVA	11.3	21.5	22.5	23.4	13	24.4	13.6	25.5	14.2	21.6	22.1	44	23.4	24.4	48	25.5
		LV Amps	119	212	212	212	119	212	119	212	119	106	106	200	106	106	200	106
11	Federal	HV Amps	156	312	312	312	156	312	156	312	156	156	156	312	156	156	313	156
		kVA	18.8	35.9	37.5	39	21.8	40.7	22.8	42.5	23.8	35.9	36.8	73.3	39	40.7	80	42.5
		LV Amps	198	354	354	354	198	354	198	354	198	177	177	333	177	177	333	177

Group 3 - 240x480 Input, 24/48 Output

	Models by Brand	Line Voltage	200	208	220	230	240	380	416	430	435	436	440	440	450	456	460	480
	Models by Brand	Load Voltage	220	229	242	276	264	418	458	473	457	480	462	484	473	479	483	504
Connection Diagram			1	1	1	2	1	4	4	4	3	4	3	4	3	3	3	3
1	Federal	HV Amps	2.08	2.08	2.08	1.04	2.08	1.04	1.04	1.04	2.08	1.04	2.08	1.04	2.08	2.08	2.08	2.08
		kVA	0.46	0.48	0.5	0.29	0.55	0.44	0.48	0.49	0.95	0.5	0.96	0.5	0.98	1	1.01	1.05
		LV Amps	2.29	2.29	2.29	1.25	2.29	1.15	1.15	1.15	2.19	1.15	2.19	1.15	2.19	2.19	2.19	2.19
2	Federal	HV Amps	4.17	4.17	4.17	2.08	4.17	2.08	2.08	2.08	4.17	2.08	4.17	2.08	4.17	4.17	4.17	4.17
		kVA	0.92	0.95	1.01	0.58	1.1	0.87	0.95	0.99	1.9	1	1.93	1.01	1.97	2	2.01	2.1
		LV Amps	4.58	4.58	4.58	2.5	4.58	2.29	2.29	2.29	4.38	2.29	4.38	2.29	4.38	4.38	4.38	4.38
4	Federal	HV Amps	6.25	6.25	6.25	3.13	6.25	3.13	3.13	3.13	6.25	3.13	6.25	3.13	6.25	6.25	6.25	6.25
		kVA	1.38	1.43	1.51	0.86	1.65	1.31	1.43	1.48	2.85	1.5	2.89	1.51	2.95	2.99	3.02	3.15
		LV Amps	6.88	6.88	6.88	3.75	6.88	3.44	3.44	3.44	6.56	3.44	6.56	3.44	6.56	6.56	6.56	6.56
5	Federal	HV Amps	10.4	10.4	10.4	5.21	10.4	5.21	5.21	5.21	10.4	5.21	10.4	5.21	10.4	10.4	10.4	10.4
		kVA	2.29	2.38	2.52	1.44	2.75	2.18	2.38	2.46	4.76	2.5	4.81	2.52	4.92	4.99	5.03	5.25
		LV Amps	11.5	11.5	11.5	6.3	11.5	5.73	5.73	5.73	10.9	5.73	10.9	5.73	10.9	10.9	10.9	10.9
6	Federal	HV Amps	20.8	20.8	20.8	10.4	20.8	10.4	10.4	10.4	20.8	10.4	20.8	10.4	20.8	20.8	20.8	20.8
		kVA	4.58	4.77	5.04	2.88	5.5	4.35	4.77	4.93	9.52	5	9.63	5.04	9.84	9.98	10.1	10.5
		LV Amps	22.9	22.9	22.9	12.5	22.9	11.5	11.5	11.5	21.9	11.5	21.9	11.5	21.9	21.9	21.9	21.9
7	Federal	HV Amps	31.3	31.3	31.3	15.6	31.3	15.6	15.6	15.6	31.3	15.6	31.3	15.6	31.3	31.3	31.3	31.3
		kVA	6.88	7.15	7.56	4.31	8.25	6.53	7.15	7.39	14.3	7.49	14.4	7.56	14.8	15	15.1	15.8
		LV Amps	34.4	34.4	34.4	18.8	34.4	17.2	17.2	17.2	32.8	17.2	32.8	17.2	32.8	32.8	32.8	32.8
8	Federal	HV Amps	41.7	41.7	41.7	20.8	41.7	20.8	20.8	20.8	41.7	20.8	41.7	20.8	41.7	41.7	41.7	41.7
		kVA	9.17	9.53	10.1	5.75	11	8.71	9.53	9.85	19	9.99	19.3	10.1	19.7	20	20.1	21
		LV Amps	45.8	45.8	45.8	25	45.8	22.9	22.9	22.9	43.8	22.9	43.8	22.9	43.8	43.8	43.8	43.8
9	Federal	HV Amps	62.5	62.5	62.5	31.3	62.5	31.3	31.3	31.3	62.5	31.3	62.5	31.3	62.5	62.5	62.5	62.5
		kVA	13.8	14.3	15.1	8.6	16.5	13.1	14.3	14.8	28.5	15	28.9	15.1	29.5	29.9	30.2	31.5
		LV Amps	68.8	68.8	68.8	37.5	68.8	34.4	34.4	34.4	65.6	34.4	65.6	34.4	65.6	65.6	65.6	65.6
10	Federal	HV Amps	83.3	83.3	83.3	41.7	83.3	41.7	41.7	41.7	83.3	41.7	83.3	41.7	83.3	83.3	83.3	83.3
		kVA	18.3	19.1	20.2	11.5	22	17.4	19.1	19.7	38.1	20	38.5	20.2	39.4	39.9	40.3	42
		LV Amps	91.7	91.7	91.7	50	91.7	45.8	45.8	45.8	87.5	45.8	87.5	45.8	87.5	87.5	87.5	87.5
11	Federal	HV Amps	125	125	125	62.5	125	62.5	62.5	62.5	125	62.5	125	62.5	125	125	125	125
		kVA	27.5	28.6	30.3	17.3	33	26.1	28.6	29.6	57.1	30	57.8	30.3	59.1	59.9	60.4	63
		LV Amps	138	138	138	75	138	68.8	68.8	68.8	131	68.8	131	68.8	131	131	131	131
12	Federal	HV Amps	208	208	208	104	208	104	104	104	208	104	208	104	208	208	208	208
		kVA	45.8	47.7	50.4	28.8	55	43.5	47.7	49.3	95.2	50	96.3	50.4	98.4	99.8	101	105
		LV Amps	229	229	229	125	229	115	115	115	219	115	219	115	219	219	219	219

Product Selection - 3 Phase Buck Boosts

Group 1 - 120x240 Input, 12/24 Output

	Models by Brand	Line Voltage	189	198	208	208	220	227	228	232	240	189Y 109	199Y 115	208Y 120	379Y 219	416Y 240	416Y 240
	Models by Brand	Load Voltage	208	208	218	229	242	250	239	255	264	208Y 120	239Y 138	229Y 132	417Y 241	436Y 252	457Y 264
Quantity Required			2	2	2	2	2	2	2	2	2	3	3	3	3	3	3
Connection Diagram			7	8	8	7	7	7	8	7	7	10	9	10	12	11	12
1	Federal	HV Amps	2.08	4.17	4.17	2.08	2.08	2.08	4.17	2.08	2.08	4.17	2.08	4.17	2.08	4.17	2.08
		kVA	0.76	1.51	1.58	0.83	0.88	0.91	1.73	0.93	0.96	1.5	0.86	1.65	1.51	3.15	1.65
		LV Amps	2.29	4.38	4.38	2.29	2.29	2.29	4.38	2.29	2.29	4.58	2.5	4.58	2.29	4.38	2.29
2	Federal	HV Amps	4.17	8.33	8.33	4.17	4.17	4.17	8.33	4.17	4.17	8.33	4.17	8.33	4.17	8.33	4.17
		kVA	1.51	3.01	3.16	1.66	1.75	1.81	3.46	1.85	1.91	3	1.73	3.3	3.01	6.3	3.3
		LV Amps	4.58	8.75	8.75	4.58	4.58	4.58	8.75	4.58	4.58	9.17	5	9.17	4.58	8.75	4.58
3	Federal	HV Amps	6.25	12.5	12.5	6.25	6.25	6.25	12.5	6.25	6.25	12.5	6.25	12.5	6.25	12.5	6.25
		kVA	2.26	4.51	4.73	2.48	2.62	2.71	5.19	2.77	2.86	4.5	2.59	4.95	4.52	9.45	4.95
		LV Amps	6.88	13.1	13.1	6.88	6.88	6.88	13.1	6.88	6.88	13.8	7.5	13.8	6.88	13.1	6.88
4	Federal	HV Amps	10.4	20.8	20.8	10.4	10.4	10.4	20.8	10.4	10.4	20.8	10.4	20.8	10.4	20.8	10.4
		kVA	3.76	7.51	7.89	4.13	4.37	4.51	8.64	4.61	4.77	7.5	4.31	8.25	7.53	15.75	8.25
		LV Amps	11.5	21.9	21.9	11.5	11.5	11.5	21.9	11.5	11.5	22.9	12.5	22.9	11.5	21.9	11.5
5	Federal	HV Amps	20.8	41.7	41.7	20.8	20.8	20.8	41.7	20.8	20.8	41.7	20.8	41.7	20.8	41.7	20.8
		kVA	7.51	15	15.8	8.26	8.74	9.02	17.3	9.21	9.53	15	8.6	16.5	15.1	31.5	16.5
		LV Amps	22.9	43.8	43.8	22.9	22.9	22.9	43.8	22.9	22.9	45.8	25	45.8	22.9	43.8	22.9
6	Federal	HV Amps	31.3	62.5	62.5	31.3	31.3	31.3	62.5	31.3	31.3	62.5	31.3	62.5	31.3	62.5	31.3
		kVA	11.3	22.5	23.7	12.4	13.1	13.5	25.9	13.8	14.3	22.5	12.9	24.8	22.6	47.3	24.8
		LV Amps	34.4	65.6	65.6	34.4	34.4	34.4	65.6	34.4	34.4	68.8	37.5	68.8	34.4	65.6	34.4
7	Federal	HV Amps	41.7	83.3	83.3	41.7	41.7	41.7	83.3	41.7	41.7	83.3	41.7	83.3	41.7	83.3	41.7
		kVA	15	30	31.5	16.5	17.5	18	34.6	18.4	19.1	30	17.3	33	30.1	63	33
		LV Amps	45.8	87.5	87.5	45.8	45.8	45.8	87.5	45.8	45.8	91.7	50	91.7	45.8	87.5	45.8
8	Federal	HV Amps	62.5	125	125	62.5	62.5	62.5	125	62.5	62.5	125	62.5	125	62.5	125	62.5
		kVA	22.5	45	47.3	24.8	26.2	27	51.8	27.6	28.6	45	25.9	49.5	45.2	94.5	49.5
		LV Amps	68.8	131	131	68.8	68.8	68.8	131	68.8	68.8	138	75	138	68.8	131	68.8
9	Federal	HV Amps	83.3	167	167	83.3	83.3	83.3	167	83.3	83.3	167	83.3	167	83.3	167	83.3
		kVA	30	60	63.1	33	34.9	36.1	69.1	36.8	38.1	60	34.5	66	60.3	126	66
		LV Amps	91.7	175	175	91.7	91.7	91.7	175	91.7	91.7	183	100	183	91.7	175	91.7
10	Federal	HV Amps	125	250	250	125	125	125	250	125	125	250	125	250	125	250	125
		kVA	45	90	94.6	49.5	52.4	54.1	103.7	55.3	57.2	90	51.8	99	90.4	189	99
		LV Amps	138	263	263	138	138	138	263	138	138	275	150	275	138	263	138
11	Federal	HV Amps	208	417	417	208	208	208	417	208	208	417	208	417	208	417	208
		kVA	75	150	157.6	82.6	87.3	90.1	172.8	92.1	95.3	150	86.3	165	151	315	165
		LV Amps	229	438	438	229	229	229	438	229	229	458	250	458	229	438	229

Group 2 - 120x240 Input, 16/32 Output

	Models by Brand	Line Voltage	184	195	208	208	225	230	234	234	240	240	184Y 106	416Y 240	379Y 219	416Y 240	416Y 240
	Models by Brand	Load Voltage	209	208	222	236	240	245	250	265	272	256	208Y 120	236Y 136	431Y 249	443Y 256	471Y 272
Quantity Required			2	2	2	2	2	2	2	2	2	2	3	3	3	3	3
Connection Diagram			7	8	8	7	8	8	8	7	7	8	10	10	12	11	12
1	Federal	HV Amps	1.56	3.13	3.13	1.56	3.13	3.13	3.13	1.56	1.56	3.13	3.13	3.13	1.56	3.13	1.56
		kVA	0.57	1.13	1.21	0.64	1.3	1.33	1.36	0.72	0.74	1.39	1.13	1.28	1.17	2.4	1.28
		LV Amps	1.77	3.33	3.33	1.77	3.33	3.33	3.33	1.77	1.77	3.33	3.54	3.54	1.77	3.33	1.77
2	Federal	HV Amps	3.13	6.25	6.25	3.13	6.25	6.25	6.25	3.13	3.13	6.25	6.25	6.25	3.13	6.25	3.13
		kVA	1.13	2.26	2.41	1.28	2.6	2.66	2.71	1.44	1.48	2.78	2.25	2.55	2.33	4.8	2.55
		LV Amps	3.54	6.67	6.67	3.54	6.67	6.67	6.67	3.54	3.54	6.67	7.08	7.08	3.54	6.67	3.54
3	Federal	HV Amps	4.69	9.38	9.38	4.69	9.38	9.38	9.38	4.69	4.69	9.38	9.38	9.38	4.69	9.4	4.69
		kVA	1.7	3.38	3.61	1.92	3.9	3.99	4.06	2.16	2.21	4.16	3.38	3.83	3.5	7.2	3.83
		LV Amps	5.31	10	10	5.31	10	10	10	5.31	5.31	10	10.6	10.6	5.31	10	5.31
4	Federal	HV Amps	7.81	15.6	15.6	7.8	15.6	15.6	15.6	7.81	7.81	15.6	15.6	15.6	7.81	15.6	7.81
		kVA	2.83	5.63	6.01	3.19	6.5	6.64	6.76	3.59	3.69	6.93	5.63	6.38	5.84	12	6.38
		LV Amps	8.85	16.7	16.7	8.9	16.7	16.7	16.7	8.85	8.85	16.7	17.7	17.7	8.85	16.7	8.85
5	Federal	HV Amps	15.6	31.3	31.3	15.6	31.3	31.3	31.3	15.6	15.6	31.3	31.3	31.3	15.6	31.3	15.6
		kVA	5.65	11.3	12	6.38	13	13.3	13.5	7.18	7.37	13.9	11.3	12.8	11.7	24	12.8
		LV Amps	17.7	33.3	33.3	17.7	33.3	33.3	33.3	17.7	17.7	33.3	35.4	35.4	17.7	33.3	17.7
6	Federal	HV Amps	23.4	46.9	46.9	23.4	46.9	46.9	46.9	23.4	23.4	46.9	46.9	46.9	23.1	46.9	23.4
		kVA	8.47	16.9	18	9.57	19.5	19.9	20.3	10.8	11.1	20.8	16.9	19.1	17.5	36	19.1
		LV Amps	26.6	50	50	26.6	50	50	50	26.6	26.6	50	53.1	53.1	26.6	50	26.6
7	Federal	HV Amps	31.3	62.5	62.5	31.3	62.5	62.5	62.5	31.3	31.3	62.5	62.5	62.5	31.3	62.5	31.3
		kVA	11.3	22.5	24	12.8	26	26.6	27	14.4	14.7	27.7	22.5	25.5	23.3	48	25.5
		LV Amps	35.4	66.7	66.7	35.4	66.7	66.7	66.7	35.4	35.4	66.7	70.8	70.8	35.4	66.7	35.4
8	Federal	HV Amps	46.9	93.8	93.8	46.9	93.8	93.8	93.8	46.9	46.9	93.8	93.8	93.8	46.9	93.8	46.9
		kVA	16.9	33.8	36	19.1	39	39.8	40.5	21.5	22.1	41.6	33.8	38.3	35	72	38.3
		LV Amps	53.1	100	100	53.1	100	100	100	53.1	53.1	100	106	106	53.1	100	53.1
9	Federal	HV Amps	62.5	125	125	62.5	125	125	125	62.5	62.5	125	125	125	62.5	125	62.5
		kVA	22.6	45	48	25.5	52	53.1	54	28.7	29.4	55.4	45	51	46.7	96	51
		LV Amps	70.8	133.3	133.3	70.8	133.3	133.3	133.3	70.8	70.8	133.3	142	142	70.8	133	70.8
10	Federal	HV Amps	93.75	187.5	187.5	93.75	187.5	187.5	187.5	93.75	93.75	187.5	188	188	93.8	188	93.8
		kVA	33.9	67.6	72.1	38.3	78	79.7	81.1	43.1	44.2	83.1	67.5	76.5	70	144	76.5
		LV Amps	106.3	200	200	106.3	200	200	200	106.3	106.3	200	213	213	106	200	106
11	Federal	HV Amps	156.25	312.5	312.5	156.25	313	312.5	312.5	156.25	156.25	312.5	313	313	156	313	156
		kVA	56.4	112.6	120.1	63.8	129.9	132.8	135.1	71.8	73.6	138.6	113	128	117	240	128
		LV Amps	177.1	333.3	333.3	177.1	333.3	333.3	333.3	177.1	177.1	333.3	354	354	177	333	177

Group 3 - 240x480 Input, 24/48 Output

	Models by Brand	Line Voltage	173	200	208	362	380	400	419	436	457	480	480	346Y 200	379Y 219	400Y 231	416Y 240
	Models by Brand	Load Voltage	208	240	250	380	418	440	440	480	480	528	504	416Y 240	456Y 263	480Y 277	499Y 288
Quantity Required			2	2	2	2	2	2	2	2	2	2	2	3	3	3	3
Connection Diagram			5	5	5	6	7	7	8	7	8	7	8	9	9	9	9
1	Federal	HV Amps	1.04	1.04	1.04	2.08	1.04	1.04	2.08	1.04	2.08	1.04	2.08	1.04	1.04	1.04	1.04
		kVA	0.38	0.44	0.46	1.44	0.76	0.8	1.67	0.87	1.82	0.96	1.82	0.75	0.82	0.87	0.9
		LV Amps	1.25	1.25	1.25	2.29	1.15	1.15	2.29	1.15	2.29	1.15	2.19	1.25	1.25	1.25	1.15
2	Federal	HV Amps	2.08	2.08	2.08	4.17	2.08	2.08	4.17	2.08	4.17	2.08	4.17	2.08	2.08	2.08	2.08
		kVA	0.75	0.87	0.91	2.88	1.51	1.59	3.33	1.74	3.63	1.91	3.64	1.5	1.64	1.73	1.8
		LV Amps	2.5	2.5	2.5	4.58	2.29	2.29	4.58	2.29	4.58	2.29	4.38	2.5	2.5	2.5	2.5
3	Federal	HV Amps	3.13	3.13	3.13	6.25	3.13	3.13	6.25	3.13	6.25	3.13	6.25	3.13	3.13	3.13	3.13
		kVA	1.13	1.3	1.36	4.32	2.27	2.39	4.99	2.6	5.45	2.86	5.46	2.25	2.47	2.6	2.7
		LV Amps	3.75	3.75	3.75	6.88	3.44	3.44	6.88	3.44	6.88	3.44	6.56	3.75	3.75	3.75	3.75
4	Federal	HV Amps	5.21	5.21	5.21	10.4	5.21	5.21	10.4	5.21	10.4	5.21	10.4	5.21	5.21	5.21	5.21
		kVA	1.88	2.17	2.26	7.19	3.78	3.97	8.32	4.33	9.07	4.77	9.1	3.75	4.11	4.33	4.56
		LV Amps	6.25	6.25	6.25	11.5	5.73	5.73	11.5	5.73	11.5	5.73	10.9	6.25	6.25	6.25	6.25
5	Federal	HV Amps	10.4	10.4	10.4	20.8	10.4	10.4	20.8	10.4	20.8	10.4	20.8	10.4	10.4	10.4	10.4
		kVA	3.75	4.34	4.51	14.4	7.55	7.94	16.6	8.66	18.1	9.53	18.2	7.5	8.22	8.66	9
		LV Amps	12.5	12.5	12.5	22.9	11.5	11.5	22.9	11.5	22.9	11.5	21.9	12.5	12.5	12.5	12.5
6	Federal	HV Amps	15.6	15.6	15.6	31.3	15.6	15.6	31.3	15.6	31.3	15.6	31.3	15.6	15.6	15.6	15.6
		kVA	5.62	6.5	6.76	21.6	11.3	11.9	25	13	27.2	14.3	27.3	11.3	12.3	13	13.5
		LV Amps	18.8	18.8	18.8	34.4	17.2	17.2	34.4	17.2	34.4	17.2	32.8	18.8	18.8	18.8	18.8
7	Federal	HV Amps	20.8	20.8	20.8	41.7	20.8	20.8	41.7	20.8	41.7	20.8	41.7	20.8	20.8	20.8	20.8
		kVA	7.5	8.67	9.01	28.7	15.1	15.9	33.3	17.3	36.3	19.1	36.4	15	16.4	17.3	18
		LV Amps	25	25	25	45.8	22.9	22.9	45.8	22.9	45.8	22.9	43.8	25	25	25	25
8	Federal	HV Amps	31.3	31.3	31.3	62.5	31.3	31.3	62.5	31.3	62.5	31.3	62.5	31.3	31.3	31.3	31.3
		kVA	11.2	13	13.5	43.1	22.6	23.8	49.9	26	54.4	28.6	54.6	22.5	24.7	26	27
		LV Amps	37.5	37.5	37.5	68.8	34.4	34.4	68.8	34.4	68.8	34.4	65.6	37.5	37.5	37.5	37.5
9	Federal	HV Amps	41.7	41.7	41.7	83.3	41.7	41.7	83.3	41.7	83.8	41.7	83.3	41.7	41.7	41.7	41.7
		kVA	15	17.3	18	57.5	30.2	31.8	66.5	34.6	72.6	38.1	72.8	30	32.9	34.6	36
		LV Amps	50	50	50	91.7	45.8	45.8	91.7	45.8	91.7	45.8	87.5	50	50	50	50
10	Federal	HV Amps	62.5	62.5	62.5	125	62.5	62.5	125	62.5	125	62.5	125	62.5	62.5	62.5	62.5
		kVA	22.5	26	27	86.2	45.3	47.6	99.8	51.9	109	57.2	109	45	49.3	51.9	54
		LV Amps	75	75	75	138	68.8	68.8	138	68.8	138	68.8	131	75	75	75	75
11	Federal	HV Amps	104	104	104	208	104	104	208	104	208	104	208	104	104	104	104
		kVA	37.5	43.3	45	144	75.4	79.4	166	86.5	181	95.3	182	75	82.2	86.6	90
		LV Amps	125	125	125	229	115	115	229	115	229	115	219	125	125	125	125

FAQ

Applications

1.What is a buck boost transformer?

Buck-boost transformers are small single phase transformers designed to reduce (buck) or raise (boost) line voltage from 5 - 20%. The most common example is boosting 208 volts to 230 volts, usually to operate a 230 volt motor such as an airconditioner compressor, from a 208 volt supply line.

Buck-boosts are a standard type of single phase distribution transformers, with primary voltages of 120, 240 or 480 volts and secondaries typically of 12, 16, 24, 32 or 48 volts. They are available in sizes ranging from 50 volt amperes to 10 kilo-volt amperes.

Buck-boost transformers are shipped ready to be connected for a number of possible voltage combinations.

2. Where Are Buck-Boost Transformers Used?

A typical buck boost application is 120 volts in, 12 volts out for low voltage lighting or control circuitry. In most applications, this low voltage transformer is field connected as an autotransformer. (See question 2 for the definition of an autotransformer). Buck-boost transformers provide tremendous capabilities and flexibility in KVA sizes and input/output voltage combinations. Basically, you get 75 different transformers, all in one convenient package.

Other buck boost applications are, where (A) low supply voltage exists because equipment is installed at the end of a bus system; (B) the supply system is operating at or over its design capacity; and (C) where overall consumer demands may be so high the utility cuts back the supply voltage to the consumer causing a "brownout."

Why Use Buck-Boost Instead of Another Type Transformer?

Take a look at the advantages and disadvantages of using a buck boost transformer (autotransformer) compared to a standard isolation transformer of the proper size and voltage combination.

As you can see, the advantages are many, the economies great. Buck- boost transformers are readily available from the stock of your nearest Power Distribution Products Distributor.

ADVANTAGESDISADVANTAGES

More efficient	No circuit isolation
Smaller & lighter	Cannot create a neutral
5-10 times increase in KVA	Application voltage and the KVA don't match the nameplate voltages and KVA
Versatile, many applications	-
Lower cost	-

Proper Voltage Is Critical

With nearly two-thirds of all electrical loads being A.C. motor loads, maintenance of the proper voltage to that motor is very important. If the supply line voltage is not maintained, motor winding current is increased causing reduced motor torque and escalating motor temperature, all of which results in the rapid loss of insulation life expectancy.

In addition to motor loads, the detrimental effects of low voltage on both resistive heating loads and incandescent lighting output is illustrated in the chart.

Anytime you have a lower than standard voltage, equipment damage and failure can result.

Buck-boost transformers are an economical way to correct this potentially very serious problem. Anytime a line voltage change in the 5-20% range is required, a buck boost transformer should be considered as your first line of defense.

3. How does a buck boost transformer differ from an insulating transformer?

A buck boost transformer IS an insulating type transformer when it is shipped from the factory. When it is connected at the job site, a lead wire on the primary is connected to a lead wire on the secondary - thereby changing the transformer's electrical characteristics to those of an autotransformer. The primary and secondary windings are no longer "insulated" and secondary windings are no longer "insulated" and its KVA capacity is greatly increased.

4. What is the difference between a buckboost transformer and an autotransformer?

When a primary lead wire and secondary lead wire of a buckboost transformer are connected together electrically, in a recommended voltage bucking or boosting connection, the transformer is in all respects, an autotransformer. However, if the interconnection between the primary and secondary winding is not made, then the unit is an insulating type transformer.

5. Why are they used?

Electrical and electronic equipment is designed to operate on standard supply voltage. When the supply voltage is constantly too high or too low, (usually more than 55%), the equipment fails to operate at maximum efficiency. A buck and boost transformer is a simple and ECONOMICAL means of correcting this off-standard voltage.

6. What are the most common applications for buck boost transformers?

Boosting 208V to 230V or 240V and vice versa for commercial and industrial air conditioning systems; boosting 110V to 120V and 240V to 277V for lighting systems; voltage correction for heating systems and induction motors of all types. Many applications exist where supply voltages are constantly above or below normal.

7. Can buck boost transformers be used to power low voltage circuits?

Yes, low voltage control, lighting circuits, or other low voltage applications requiring either 12V, 16V, 24V, 32V or 48V. The unit is connected as an insulating transformer and the nameplate KVA rating is the transformer's capacity.

Operation and Construction

8. Why do buck boost transformers have 4 windings?

To make them versatile! A four winding buck boost transformer (2 primary and 2 secondary windings) can be connected eight different ways to provide a multitude of voltage and KVA outputs. A two winding (1 primary & 1 secondary) buck boost transformer can be connected only one way.

9. Will a buck boost transformer stabilize voltage?

No. The output voltage is a function of the input voltage. If the input voltage varies, then the output voltage will also vary by the same percentage.

Load Data

10. Are there any restrictions on the type of load that can be operated from a buck boost transformer?

No, there are no restrictions.

11. Why can a buck boost transformer operate a KVA load many times larger than the KVA rating on its nameplate?

Since the transformer has been auto-connected in such a fashion that the 22V secondary voltage is added to the 208V primary voltage, it produces 230V output.

The autotransformer KVA is calculated:

KVA =	Output Volts x Secondary Amps
	1000

KVA =	230 V x 41.67 Amps = 9.58 KVA
	1000

12. Can buck boost transformers be used on motor loads?

Yes, either single or three phase. Refer to the motor data charts in Section I for determining KVA and Amps required by NEMA standard motors.

13. How are single phase and three phase load Amps and load KVA calculated?

Single phase Amps =	KVA x 1000
	Volts

Three phase Amps =	KVA x 1000
	Volts x 1.73

Single phase KVA =	Volts x Amps
	1000

Three phase KVA =	Volts x Amps x 1.73
	1000

Three-Phase

14. Can buck boost transformers be used on three-phase systems as well as single phase systems?

Yes. A single unit is used to buck or boost single phase voltage - two or three units are used to buck or boost three phase voltage. The number of units to be used in a three -phase installation depends on the number of wires in the supply line. If the three-phase supply is 4 wire Y, use three buck boost transformers. If the 3 - phase supply is 3 wire Y (neutral not available), use two buck boost transformers. Refer to three-phase selection charts.

15. Should buck boost transformers be used to develop a three-phase 4 wire Y circuit from a three-phase 3 wire delta circuit?

No. A three phase "wye" buck boost transformer connection should be used only on a 4 wire source of supply. A delta to wye connection does not provide adequate current capacity to accommodate unbalanced currents flowing in the neutral wire of the 4 wire circuit.

3 PHASE CONNECTIONS
INPUT (SUPPLY SYSTEM)	DESIRED OUTPUT CONNECTION
DELTA 3 wire	WYE 3 or 4 wire	DO NO USE
OPEN DELTA 3 wire	WYE 3 or 4 wire	DO NOT USE
WYE 3 or 4 wire	CLOSED DELTA 3 wire	DO NOT USE
WYE 4 wire	WYE 3 or 4 wire	OK
WYE 3 or 4 wire	OPEN DELTA 3 wire	OK
CLOSED DELTA 3 wire	OPEN DELTA 3 wire	OK

16. Why isn't a closed delta buck boost connection recommended?

A closed delta buck boost auto transformer connection requires more transformer KVA than a "wye" or open delta connection and phase shifting occurs on the output. Consequently the closed delta connection is more expensive and electrically inferior to other three-phase connections.

Connection and Frequency

17. How does the installer or user know how to connect a buck boost transformer?

The connection chart (for Acme and Federal) packed with each unit shows how to make the appropriate connections.

18. Can 60 Hertz buck boost transformers be used on a 50 Hertz service?

No. Acme buck boost transformers should be operated only at the frequencies recommended. However, units recommended for 50 cycle operation are suitable for 60 cycle operation but not vice versa.

Selection

19. How do you select a buck boost transformer?

Refer to the selection steps below for easy 4-step selection, then go to the charts.

Nameplate Data

20. Why are buck boost transformers shipped from the factory as insulating transformers and not preconnected at the factory as autotransformers?

A four winding buck boost transformer can be auto connected eight different ways to provide a multitude of voltage and KVA output combinations. The proper transformer connection depends on the user's supply voltage, load voltage and load KVA. Consequently, it is more feasible for the manufacturer to ship the unit as an insulating transformer and allow the user to connect it on the job site in accordance with the available supply voltage and requirements of his load.

21. Why is the isolation transformer KVA rating shown on the nameplate instead of the autotransformer KVA rating?

The KVA rating of a buck boost transformer when auto connected depends on the amount of voltage buck or boost. Since the amount of voltage buck or boost is different for each connection, it is physically impossible to show all of the various voltage combinations and attainable KVA ratings on the nameplate. A connection chart showing the various attainable single phase and three-phase connections is packed with each unit.

Safety

22. Do buck boost transformers present a safety hazard usually associated with autotransformers?

No. Most autotransformers, if they are not of the buck boost variety, change voltage from one voltage class to another. (Example 480V to 240V) In a system where one line is grounded, the user thinks he has 240V; yet due to the primary and secondary being tied together, it is possible to have 480V to ground from the 240V output. A buck boost transformer only changes the voltage a small amount, such as 208V to 240V. This small increase does not represent a safety hazard, as compared to a buck of 480V to 240V.

Sound Levels

23. Are buck boost transformers as quiet as standard isolation transformers?

Yes. However, an auto-connected buck boost transformer will be quieter than an isolation transformer capable of handling the same load. The isolation transformer would have to be physically larger than the buck boost transformer, and small transformers are quieter than larger ones. (Example) 1 KVA - 40 db; 75 KVA - 50 db. (db is a unit of sound measure).

Cost and Life Expectancy

24. How does the cost of a buck boost transformer compare to that of an insulating transformer - both capable of handling the same load?

For the most common buck boost applications, the dollar savings are generally greater than 75% compared to the use of an insulating type distribution transformer for the same application.

25. What is the life expectancy of a buck boost transformer?

The life expectancy of a buck boost transformer is the same as the life expectancy of other dry type transformers.

National Electrical Code

26. It is indicated that a buck boost transformer is suitable for connecting as an autotransformer. What is the definition of an autotransformer and how does it differ from an isolation transformer?

An autotransformer is a transformer in which the primary (input) and the secondary (output) are electrically connected to each other. An isolation transformer, also known as an insulating transformer, has complete electrical separation between the primary (input) and the secondary (output).

An autotransformer changes or transforms only a portion of the electrical energy it transmits. The rest of the electrical energy flows directly through the electrical connections between the primary and secondary. An isolation transformer (insulating transformer) changes or transforms all of the electrical energy it transmits.

Consequently, an autotransformer is smaller, lighter in weight, and less costly than a comparable KVA size insulating transformer. Please refer to Question 27 for additional information on autotransformers.

Buck-boost transformers are frequently field-connected as autotransformers.

27. Buck-boost transformers are almost always installed as auto-transformers. Does the N.E.C. (National Electrical Code) permit the use of autotransformers?

Yes. Please refer to N.E.C. Article 450-4, "Autotransformers 600 Volts, Nominal, or Less." Item (a) explains how to overcurrent protect an autotransformer; item (b) explains that an insulating transformer such as a buck boost transformer may be field connected as an autotransformer.

28. When a buck boost is connected as an autotransformer such as boosting 208V to 230V, the KVA is greatly increased. How do you determine the size (ampere rating) of the overcurrent protective device (such as a fuse or circuit breaker)?

The National Electrical Code Article 450-4 addresses overcurrent protection of autotransformers. A copy is reproduced below for easy reference.

450-4. Autotransformers 600 Volts, Nominal, or Less.

(a) Overcurrent Protection. Each autotransformer 600 volts, nominal, or less shall be protected by an individual overcurrent device installed in series with each ungrounded input conductor. Such overcurrent device shall be rated or set at not more than 125 percent of the rated full-load input current of the autotransformer. An overcurrent device shall not be installed in series with the shunt winding (the winding common to both the input and the output circuits) of the autotransformer between Points A and B as shown in Diagram 450-4.

Exception: Where the rated input current of an autotransformer is 9 amperes or more and 125 percent of this current does not correspond to a standard rating of a fuse or non-adjustable circuit breaker, the next higher standard rating described in Section 240-6 shall be permitted. When the rated input current is less than 9 amperes, an overcurrent device rated or set at not more than 167 percent of the input current shall be permitted.

(b) Transformer Field-Connected as an Autotransformer. A transformer field-connected as an autotransformer shall be identified for use at elevated voltage.

An example of an everyday application is always a good way to explain the intent of the "Code."

Example: A 1 KVA transformer Catalog No. Acme has a primary of 120 x 240V and a secondary of 12 x24V. It is to be connected as an autotransformer at the time of installation to raise 208V to 230V single phase.

When this 1 KVA unit is connected as an autotransformer for this voltage combination, its KVA rating is increased to 9.58 KVA (may also be expressed as 9,580 VA). This is the rating to be used for determining the full load input amps and the sizing of the overcurrent protect device (fuse or breaker) on the input.

Full Load Input Amps=	9,580 Volt Amps	=46 Amps
	208 Volts

When the full load current is greater than 9 amps, the overcurrent protective device (usually a fuse or non-adjustable breaker) amp rating can be up to 125 percent of the full load rating of the autotransformer input amps.

Max. amp rating of the
overcurrent device

= 46 amps x 125% = 57.5 amps

The National Electrical Code, Article 450-4 (a) Exception, permits the use of the next higher standard ampere rating of the overcurrent device. This is shown in Article 240-6 of the N.E.C.

Max. size of the fuse or circuit breaker = 60 amps

Buck Boost Transformer Selection Guide