240v delta center tap - Milton Storm Service

J

Jimcassidy

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Location
Texas
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Retired electrician
Helping here in Florida - we have a church service that is down. I arrived late last night and will take a look at the service but I’m told it is a 240 V delta center tap, 3 phase 4 wire. Our generator has many configurations - but not 240 V delta center tap.

The service has a gutter with a current transformer type meter that has 4 -3 pole disconnects tapped from a gutter.

I’d like to give them temporary power for their worship service tomorrow & connect our 230 kV generator - what advice would you give?

I am an old electrician who went through my apprenticeship in the 1980’s. Passed the my licensing again in the last year in Oklahoma as an unlimited electrician to help with a Christian Organization but have not worked in the field on a daily basis for many years.

What caution & advice would you give?
 
petersonra said:
I think you are out of luck unless you can come up with some single phase transformers for the 120 V circuits.
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I’ve got many options on the gen set - 3 phase 480 v, 3 phase 208 v, single phase 240 v. With no power on the service and it isolated - what is the issue with providing 4 wire 208 v to a few disconnects?
 
It is likely the 208/120 3 phase would suffice for your situation at least to provide lighting. You could check the 3 phase equipment such as air conditioning and see if 208 would be adequate.
 
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If you can separate the wires at the can (or somewhere). You could connect the generator 120/240 to the wires that are connected to the transformer with the center tap
Basically supplying only single phase loads.
Augie47 also posted a good idea, just remember to turn off all three phase breakers.

One other. If it's a 12 wire generator you could rewire the generator for this service, but then there are the rotation issues, putting the generator back, etc.
I know we could wire the old military generators to about any configuration if they were 12 wire.
10 wire is a no-go
 
Jimcassidy said:
I’ve got many options on the gen set - 3 phase 480 v, 3 phase 208 v, single phase 240 v. With no power on the service and it isolated - what is the issue with providing 4 wire 208 v to a few disconnects?
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It seemed likely to me the church needed a lot of 240v 3 phase or they would not have used this kind of service.

You can certainly disconnect the single phase panelboards and hook them up to a generator set up for 208 120 as long as none of the loads on the those panelboards really need 240.

It would take a fair amount of work to investigate what you can and cannot run that way, as well as determining what is the minimum level of power needed to safely operate the church.

Not sure you can do all that in one day.
 
I think we need to make sure we are all on the same page here. I am thinking the service is 240 delta with two legs set up center tapped to ground for 120 volt circuits.

I am not convinced the idea someone had of hooking up the three phase boards to a 208-120 generator is a great idea if this is the configuration.
 
At the very least I would want some kind of sketch of what is there now before I would be offering advice on what to do. There are a lot of ways this could go wrong and catching the church on fire by mistake is not impossible if it is not a well thought out plan. That would not be much help.
 
These types of generators have a voltage adjustment knob. My preferred way of doing this is Mexico voltage 125/216 or 127/220 to split the difference.

However the only 3 phase loads in a church will probably be the air conditioners and they are almost always 240/208 dual rated, even very old ones.

As stated above a lot of investigation would be required but I live in 240 delta land and smaller generators are always 208 so this kind of thing is done all the time here.
 
petersonra said:
It seemed likely to me the church needed a lot of 240v 3 phase or they would not have used this kind of service.

You can certainly disconnect the single phase panelboards and hook them up to a generator set up for 208 120 as long as none of the loads on the those panelboards really need 240.

It would take a fair amount of work to investigate what you can and cannot run that way, as well as determining what is the minimum level of power needed to safely operate the church.

Not sure you can do all that in one day.
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One of the most common reasons for a 4 wire delta high leg installation is a very small 3 phase load as compared to the single phase load. On a pole transformer bank, the transformer that supplies the high leg often has a kVA 1/3 or less than the one that supplies the 120/240 volt single phase load.
A long time ago, that is what a delta breaker was used for. It supplied the only 3 phase load in a single phase panel and the utility supply was a 4 wire high leg delta system.
 
don_resqcapt19 said:
One of the most common reasons for a 4 wire delta high leg installation is a very small 3 phase load as compared to the single phase load. On a pole transformer bank, the transformer that supplies the high leg often has a kVA 1/3 or less than the one that supplies the 120/240 volt single phase load.
A long time ago, that is what a delta breaker was used for. It supplied the only 3 phase load in a single phase panel and the utility supply was a 4 wire high leg delta system.
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We build a two pot for the scenario above with a small 3 phase load.
There are instances where a building needs single phase and a larger three phase load.
For those we build a three pot bank.
 
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