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Electrical Wiring in the Home/Portable Generator Transfer System Question



I'm in the process of getting a portable generator wired into some sort of transfer system and have a couple of questions:

1. Transfer switch Vs Interlock Kit - I'm leaning towards Interlock kit because it is cheap and gives flexibility but I would like expert feedback on the choice. One drawback seems to be that the user may accidentally go over the limit of the generator (in my case the generator has no indication of wattage used/drawn. if that were to occur my expectation is that the generator circuit will trip and there is no harm caused to the attached devices and no other safety hazard. Can you please clarify?

2. The generator has NEMA L14-30R output (with four prongs). The  generator is rated at 7000 running watts, however, the output seems to be 3600W (120v x 30A). I think this likely has to do with the second hot leg (X or Y) in the receptacle but I'm not sure. Can you please clarify how this works and if this has any implication on the choice or wiring of the transfer switch or interlock switch.

Thanks in advance.



The interlock kit is the way to go. It is inexpensive and effective. Being able to energize any circuit in your panel is a definite advantage you just have to decide in advance what circuits you will keep on during an outage, then manage what you do keep on. The worst that can happen is the CB on the generator trips. Know what your key loads draw (wattage) so you have an idea of what your generator can handle and how many of your key loads can be on at the same time with out overloading the generator.

You will use the 4 wire 30 amp twist lock receptacle on the generator not the 120 volt 30 amp twist lock.
It does indeed give you the second "hot" leg thus increasing the full 7000 watts to your panel.

The interlock kit would be the same using either twist locking receptacle.

You need the matching 30 amp 125/250 volt generator receptacle that is pre made for mounting outside. A 2 pole 30 amp breaker for your panel. 10-4 Romex run between the panel and the outdoor receptacle. The appropriate interlock kit and if the panel happens to be a newer Square D panel they make their own version of the interlock kit at half the price.

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Licensed Master Electrician (32 years) 6165B Contractor in Closter New Jersey with 40 years total experience in Residential - Commercial - Industrial work. Emergency Service - General trouble shooting and repair work - ONAN & GENERAC generator installation - Paddle fans - Kitchen & Bath exhaust fans - AC lines - Smoke detectors - Telephone lines - Cable TV lines - Computer network cabling - Exterior lighting - Recessed lighting - Security lighting - (200 - 150 - 100 amp service up grades) - Electric Heat - New circuits - New appliance hook ups - and more ! FREE ESTIMATES 201-358-1552 Fully Insured


Licensed contractor in Closter New Jersey.

"The Frank Williams School of Electrical Construction". My dear old boss is 100 ! and still going God Bless him. I started working for "Tenafly Electric" right out of high school at 19. He was tough but I learned more working for him in 8 and half years than most guys. We did mostly industrial work while doing some commercial and residential so I was fortunate to be exposed to all 3 areas of electrical construction. The guys I worked with were all good guys and I stay in touch with some of them still. Most of us went into our own buisness's which says something about the caliber of the guys I worked with. We had some interesting clients : Wella Corp. of shampoo fame, Farah Fawcett etc, I didn't buy shampoo for 10 years. It was a great place to work. Pan Am the former airline just before they went under, another great place to work, nice clean environment. C&C Metals, the largest button manufacturer in the US at that time, a not so clean environment but a very interesting place to work, lots of machine's cranking out buttons of all kinds but you had to be on your toes, it was a potentially dangerous place to be . All kinds of action going on around you.

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