# 50amp 125/250 plug requirments



## cybersnoopy (May 23, 2008)

All.

I have a home that I recently purchased that is wired w/ a disconnect for alternative power source (generator). I would like to purchase a generator for this purpose. My dilemma is that I'm not sure as to the specifications for the plug for the generator to match up w/ the plug on the disconnect panel. 

The specs on the male plug on the disconnect panel are:
50amp 125/250 w/ 3 prongs-twist lock.

Can I use a generator that has a plug specs of ?
30amp 120v w/ 3 prongs-twist lock.

Thanks in advance for any & all support.


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## craigwatanabe (Jan 28, 2008)

No the twist locks on a 250vac is for two phase and the one you're suggesting is for 125vac single phase. 

That 250vac twistlock is used to separate the two 125vac lines into independent 125vac services at 50-amps as well as run a single service 250vac two phase circuit.

In order to hook up a generator to your power disconnect panel, your generator must be able to run a single twin-phase 250vac service. That disconnect panel was designed to handle the load requirements of a water heater, range, stove top or electric dryer as well as every 125vac circuit in your home, in other words enough power to run the entire house.

A generator that allows for only a 30-amp 125vac output can only be hooked up to your 125vac 15 and 20 amp circuits, such as your overhead lighting, living room and bedroom circuits that uses 15-amps, or your bathroom, kitchen, garage, outdoor GFCI circuits that use 20-amps. 

Even though your generator has a 30-amp load capacity, according to your post it's only for single-phase 125vac circuits. Your water heater, elecric dryer, range, stovetop use 30-amp circuits, however that's at a two-phase 250vac circuit.

Even if your generator can put out 30-amps at 250vac two phase, it's not enough to handle even those 30-amp circuits because that generator will be running at 100% output ALL THE TIME. For example even though a Mazda 323 can go 70-MPH, but sustain that speed and the engine will fail in short order. 

A 50-amp generator gives you a 20-amp headroom. That generator will be running at 40% so it's a cakewalk for it. But a 30-amp generator is screaming along at 100% and is begging for mercy the minute you power it up.

Typically a generator rated at 30-amps at 125vac is used primarily as a construction jobsite generator to power hand tools to small table saws. 

The kinds of generators used to hook up to power disconnect boxes such as yours are rated in the class of standby power generation and are quite a bit more expensive than jobsite generators.


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