I have installed commercial generators for years but never installed one on a high leg service. Recently customer request a standby generator for a commercial office that has 3 phase 120/240 delta high leg. What is required when specifying the generator hardware? To the best of my knowledge there is no such thing as a commercially available high leg generator?
STANDBY GENERATOR HIGH LEG
- Thread starter paradise
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Spec' 240/120V 3? 4W.
Supplier should know what you mean, but for reference, many just state it as 120/240 3?.
winnie
Senior Member
- Location
- Springfield, MA, USA
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- Electric motor research
Keep in mind that a very common form of generator has a '12 lead' alternator. This has 6 separate 120-150V coils which can be connected in various ways to get pretty much any of the standard utilization connections, including 240/120V high leg delta.
The supplier may need to do some internal connecting, but this should not be a big problem.
-Jon
The supplier may need to do some internal connecting, but this should not be a big problem.
-Jon
SUPPLIER RESPONSE
SUPPLIER RESPONSE
Thanks for the tips. I talked to the supplier's (distributors) sales engineer and his said that they don't have a high leg generator. I spec'd a 120/240V 3? 4W unit.
He said that this will simply connect like any delta 3? power source NO HIGH LEG. That is a little surprising considering that I have 208 volt loads using hi leg. Maybe I need to talk to mfg engineer prior to delivery. Maybe he knows more about alternator than salesman and can pre-configure my unit at factory for a minimum of field hassle.
SUPPLIER RESPONSE
Thanks for the tips. I talked to the supplier's (distributors) sales engineer and his said that they don't have a high leg generator. I spec'd a 120/240V 3? 4W unit.
He said that this will simply connect like any delta 3? power source NO HIGH LEG. That is a little surprising considering that I have 208 volt loads using hi leg. Maybe I need to talk to mfg engineer prior to delivery. Maybe he knows more about alternator than salesman and can pre-configure my unit at factory for a minimum of field hassle.
- Location
- Placerville, CA, USA
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- Retired PV System Designer
Two big problems with his approach:
1. You will get 208 volts for your existing 240 loads.
2. Any 120/240 three wire MWBCs will change to having the neutral counted as a CCC. This may or may not cause a derating problem.
One more concern: Using your existing high leg to neutral for 208 volt loads rather than for three wire 240V three phase loads is not a good idea and causes unusual transformer loading that is often not calculated properly, especially in an open delta.
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