I have a customer (kind of odd) that wants me to install a step up transformer to get him from 112V to 122V (Don't ask me why) so in theory I can just set a 35kva (based on connected load) and run the SEU into it and SEU or SER out of it to main branch circuit panel. Does the main panel now be to be wired a sub panel or not? I'm thinking old main is now sub since I need to bond grounded conducter in transformer? Is this even allowed in residential? This one has me confused a bit. I've done plenty commercial with service into the 277/480 panel then trans then Single phase sub panel but not quite like this. Any thoughts on this ?
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Step Up Trans Residential Main
- Thread starter Cletis
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- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
If you use a boost transformer or an autotransformer, you do not have a separately derived system, so no additional bonding is needed. Connect the transformer ground lug or case to the EGC.
If you use an isolation transformer you have the choice to wire it as separately derived or not.
Make that choice and then bond or do not bond accordingly.
If you go with separately derived, most prefer to put the grounded conductor bond at the transformer rather than at the panel.
If you use an isolation transformer you have the choice to wire it as separately derived or not.
Make that choice and then bond or do not bond accordingly.
If you go with separately derived, most prefer to put the grounded conductor bond at the transformer rather than at the panel.
Last edited:
If you use a boost transformer or an autotransformer, you do not have a separately derived system, so no additional bonding is needed. Connect the transformer ground lug or case to the EGC.
If you use an isolation transformer you have the choice to wire it as separately derived or not.
Make that choice and then bond or do not bond accordingly.
If you go with separately derived, most prefer to put the grounded conductor bond at the transformer rather than at the panel.
Very well then. What would you recommend to boost up a 150 amp residential service to bring it up a notch in this scenario ?? So, the existing main service could be still a main panel or a sub panel depending on which type of transformer I use is what your saying correct ?
I usually just call acme and tell them application and they build it for me which is what I would do if I get job.
Has your customer contacted the utility. Maybe they could achieve a 10% boost within the xfmr serving the residence. Seems what you are proposing would be quite expensive. Just a thought.
They are not cooperating at all with him so they won't. The problem is he has alot of sensitive equiptment and a couple german machines that have tight tolerances so he really needs things close to the 122V leaving the main panel.
gar
Senior Member
- Location
- Ann Arbor, Michigan
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- EE
141120-2057 EST
Fundamentally you need about a 1500 VA transformer so go with 2.5 or 5 kVA to get a lower impedance. Primary 112 V with a 10 V secondary as a boost source.
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Fundamentally you need about a 1500 VA transformer so go with 2.5 or 5 kVA to get a lower impedance. Primary 112 V with a 10 V secondary as a boost source.
.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
But if you actually need 122/244 single phase three wire you will need two of those transformers.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
If you get them with a center tap on the output you would be able to adjust it to only a 5 volt boost if POCO raises the voltage a bit at some point in the future.
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