A local electrical shop tried to sell me a GE 100 amp transfer switch. My main electrical panel breaker is 125 amps.
Would this be ok?
Electrical – 100 amp transfer switch for 125 amp home
electricalelectrical-paneltransfer-switch
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This one popped up for some reason, so I'll edit in some new thoughts.
Corroded or arcing power feeds are "burn your house down" serious business. Fix immediately! Aluminum feeder wire is fine stuff, but you do need to use the anti-ox goop, and torque it correctly. Many electricians in the 80s and 90s did not get the memo. Nip it in the bud fast.
Likewise corrosion (read: arcing) on breaker contact points is absolutely unacceptable. Catch it early and you may be able to save the breaker space, otherwise that's a dead space in your panel. The #1 cause is using the wrong brand of breaker. Brand X breaker won't engage Brand Y buses with the correct contact shape or clamping force, causing the arcing.
If the panel is a goner, swap it. Let me come back to that.
The cable between main and sub doesn't need 2 breakers. It needs a breaker upstream (in the main panel) to protect the cable. A 60A breaker is correct to protect #6Cu or #4Al. At the subpanel, the cable/wire can land on main lugs (provided the subpanel is rated for 60A+) or on the subpanel's main breaker (of any rating - a smaller main protects the panel, a larger main is just a shutoff switch, which you do not need since it's in the same building.) So if the subpanel has main lugs, use them instead of backfeeding a breaker.
One more thing. If the main panel is breakered at 100A, and the cable supports 100A, and the subpanel supports 100A, then the main main breaker protects them all. You don't need any breakers for the sub. You can use thru-lugs or snap-in lugs in the main panel.
With that in mind, back to replacing the panel(s). Talk to the power company and see if your service drop/meter can support 125A. Even if not, you can order a 125A main panel and swap the main breaker to 100A.
See if you can upgrade the main-sub cable to 125A. If so, order a main panel with thru lugs, which will save 2 breaker spaces, and a 125A sub. Voila, no breakers needed, space maximized!
You can also look at the CH or QO panels, which use 3/4" high breakers, so more spaces in the same panel footprint. GFCI and AFCI breakers are available for them.
What doesn't work is "double-stuff" breakers (including GE's 1/2" Q-line breakers). Those are useless as almost all new work today requires GFCI, AFCI or both - and you cannot obtain those in double-stuff. So a "24/48" panel is actually 24, period.
Original:
Wire gauge is decided by what NEC requires (and those are in stair-steps) and what your electrical distributor has in stock.
So with numbers as close as 100A vs 125A, you might get lucky: imagine the original installer found #2 wire was good for 95A, #1 for 110A and #0 aka 1/0 was good for 125A. He can't use #2, the distributor does not stock #1, so he uses 1/0. You get a happy surprise when you aim to upgrade. Hey, it could happen - check. If not, you need to pull bigger wire.
Check the markings on the aluminum conductors to make sure they are stranded and the modern AA-8000 series alloy, which are legal and safe. (NEC 310.106b). The problem alloys from the 1950s are now outlawed, and your distributor won't even sell them.
Your reduced voltage to 108 is more likely to be a problem with your neutral. Poor connections can't drop 12 volts without destroying themselves from heat (volts x amps = watts of heat), more likely your other leg went to 132 volts because of a lost neutral. This is an extremely dangerous condition that needs to be taken out of service immediately because the imbalance can be much worse than 12V, and that will destroy appliances and start fires. If you know where the problem is, but can't de-energize your house now, a short-term work-around is disable one "hot" - doesn't matter which one. Look at how the hot busbars are arranged inside the panel, pick one leg, and remove every breaker which uses that leg. Rearrange as necessary to keep the lights on. At that point, if the neutral fails, the circuits will shut off instead of giving dangerous voltages.
Look for other options (i.e. other brands or suppliers) that will give you more spaces in the panel. You don't want to be forced into using duplex breakers, because - especially when you remodel - you'll be forced to follow current code, and will need more kitchen breakers and GFCI and AFCI breakers in many slots. Those are a lot more expensive as duplex. You can completely fill the panel with double-stuff breakers (in fact, doing so is the basis of their "48 circuit" marketing claim).
Don't buy this at the big-box home improvement stores, go to a real electrical distributor such as Greybar - they tend to be locally owned. They will have better options (eg more breaker spaces in smaller boxes, Homelites are huge), better quality and sometimes better prices. For instance, Homelite is Square D's bottom-tier brand. There's better out there, and it's worth an extra $100 to not have problems like the ones you are having.
For a generator of that size, the primary connection would not be through those convenience outlets, but rather directly to lugs sized for the cables required. If this wasn't the primary use of the generator, and you wanted an easily detachable connection, and 50 amps was sufficient, then you could use the 4-conductor receptacle with a cable.
Your model sounds like the G50. See page 34 of that manual:
3.13 Connection Lugs
See Graphic: wc_gr002611
The customer connection lugs (r) are located on left at the bottom of the panel behind a hinged door. The lugs provide connection points for attachment of outside loads. A large label like the one shown in section Terminal Connections is attached to the inside of the terminal door. It shows the correct terminal connections for selected voltages. Connections to the lugs should be made by running the power cables up under the lug door in the bottom of the panel and into the lug. Use a 3/8 in. Allen wrench to tighten cable connections in place.
Related Topic
- Electrical – Breaker panel to transfer switch
- Electrical – Add sub panel from transfer switch
- Electrical – Adding subpanel to transfer switch
- Electrical – Wire size. 125 feet underground to 100 amp sub panel
- Electrical – install 125 AMP rated sub-panel when the need is 60 AMPS
- Electrical – Generator Transfer Switch for 2 Panels
- Electrical – Generator wiring into Automatic Transfer Switch – wire gauge
Best Answer
No, you can't do that
A 100A manual transfer panel has a 100A breaker for the utility-side input; as a result, it would be a "bottleneck" if you put it inline with your service, restricting the whole service to 100A. However, this does not mean that you have the wrong transfer switch, so do not go running back to the store before you read the rest of this answer!
But, you probably don't want to transfer the entire house
Whole-house transfer sounds good at first, but especially for folks with smaller generators, its not nearly as good a plan in practice as it is in theory. Many of your larger loads, even on a smaller service, are rather large for a generator, and are not nearly as important to have on a generator unless you are dealing with a situation where the power regularly goes out for days on end. (Do you really need your dryer on a generator, or your range for that matter?) Furthermore, you will have to flip a zillion breakers in order to not overload the generator when you transfer to generator power -- probably not the easiest thing to do in the dark!
As a result, what I would do is put a 30A, 2-pole branch breaker in the main panel to provide the utility-mains-side feed to the transfer switch, and then put a subpanel in off the standby side that only has breakers in it for the critical loads -- the ability to have heat so the house doesn't freeze (with a 125A service, I can tell you do not have electric resistance heat), the ability to run a small cooking appliance (such as a plug-in electric griddle or a microwave), your refrigerator (if it's not on the aforementioned small appliance branch circuit, that is), 1-2 circuits for standby lighting + the smoke alarms and selected receptacles, and perhaps the ability to run the hot water heater as well (an electric tank-type heater can be half-volted for use on a generator at the cost of very slow recovery, as well as an extra transfer switch and some clever wiring), as well as any sump or well pumps the house may have.