buck/boost transformer

Status
Not open for further replies.
P

paul hodge

Member
Location
atl
here's the question? I have 240 primary, stepping down volyage to 208v @outlet. I have been told to install 50a 2 pole breaker @ 240v panel, with #6 feed to buck/boost transformer. Transformer data: 240/120v primary, secondary 16/32v ; transformer kva=1.5
What's your thoughts on 50a breaker.
 
Paul

If you have a handbook 450.4 (A) and (B) has some interesting commentary, I thinks the language of this section will answer most of questions as mentioned in IWIRES , the current rating on the primary winding of the buck-boost is critical

Charlie
 
Hopefully Paul will be back.

IMO it looks like a 1.5 KW buck boost transformer bucking 240 down to 212 (You won't get 208) would be appropriate for a 50 amp OCPD
 
iwire said:
Hopefully Paul will be back.

IMO it looks like a 1.5 KW buck boost transformer bucking 240 down to 212 (You won't get 208) would be appropriate for a 50 amp OCPD
Click to expand...


240-32 = 208?
 
wasasparky said:
240-32 = 208?
Click to expand...

Nevermind, I answered my own question.
You could wire the autotransformer the "nonstandard" way and get exactly 208V, but you wouldn't be able to handle as much kVA.

"Nonstandard" being put the 240V across the shunt winding only, and "subtract the secondary voltage.

"Standard" being 240V across both windings, and having the bucked voltage taken across the shunt winding...

Did the math both ways...kinda fun.
 
wasasparky said:
240-32 = 208?
Click to expand...


Transformer data: 240/120v primary, secondary 16/32v ; transformer va=1.5
The figures 16/32 are the secondary voltage when the transformer is connected as any transformer would be used.
To select the buck boost transformer you need to determine the load kva
and the required voltage. In this case its 240 to 208. Go to the MFG catalog and select the transformer required.
 
I cannot explain, but with jefferson electric buck/boost transformer connected as a autotransformer you obtain 208v.
The shop first ordered a 120/240 primary to 12/24 secondary and after repeated voltage reading, none read 208v. This was the transformer that the supply house told the shop would be correct for the application, but after studing the catolog, I thought the 16/32 secondary was correct and had shipped to jobsite and after playing with tap configurations came up with 208 secondary. Exactly 208v, from phase to phase but from phase to ground on one phase I obtain 120v, on the other phase 90v, but 208v between phase to phase.

comments?
 
steve66 said:
With a 32V secondary, it seems like you should get 240V - 32V = 208V. Can anyone explain why I don't see exactly 240V to 208V in the charts?
Steve
Click to expand...
Information taken from the Sola Web Site:

Buck-Boost transformers are small, single phase, dry type distribution
transformers designed and shipped as insulating/isolating transformers. They
have a dual voltage primary and a dual voltage secondary. These transformers can be connected for a wide range of voltage combinations. The most common use is to buck (lower) or boost (raise) the supply voltage a small amount, usually 5 to 27%. Buck-Boost transformers are in compliance with NEC Article 210-9, Exception 1 when field connected as an autotransformer.
Sola/Hevi-Duty buck-boost transformers are designed to supply power to low
voltage lighting circuits, control panels or other systems requiring 12, 16,
24, 32, or 48 Volts. When connected as an insulating transformer (by following the wiring diagram on the inside of the transformer case), the transformer's capacity matches the nameplate KVA rating."


If the transformer has a 10% buck, using 240 volts - 10% x 240 = 216 volts.





The transformers
 
bob said:
If the transformer has a 10% buck, using 240 volts - 10% x 240 = 216 volts.
Click to expand...

Actually it is 218V according to the square D calculator.

And,
Bucked voltage = Avail.Voltage / (1+%Buck)
(% buck = Vsec/Vpri of transformer)
 
paul hodge said:
here's the question? I have 240 primary, stepping down volyage to 208v @outlet. I have been told to install 50a 2 pole breaker @ 240v panel, with #6 feed to buck/boost transformer. Transformer data: 240/120v primary, secondary 16/32v ; transformer kva=1.5
What's your thoughts on 50a breaker.
Click to expand...

IWIRE was correct to ask how much load is anticipated...how much?

With the standard wiring method, if you max out what the 1500 can handle, you get about 53.2A full load. Use 60A breaker (could even go to a 70A)
 
Status
Not open for further replies.
Top