Generator wiring question

Hi,

I have a 1-1/2HP, 220v motor running from the dryer socket, all good.

I was thinking of putting in a change over switch to run the motor from the generator when the power goes out as it does regularly out here.

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To save me dragging the gen-set out and starting it to find out what is coming out of the 240-socket, thought I'd ask here.

The house wiring uses the 3-wire 110-0-110 for the 220/240 but the gen has three pins for the 240-out. I am guessing one is Ground and the others are Neutral and 240v.

How do I go about wiring that to run the motor? An ASCII diagram would be good.

Thanks

Reply to
Dave, I can't do that
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other 2 , with either hot to the neutral at 110 . Mine has a 4 wire socket , with 2 hots a neutral and a ground . I suggest you look up your model generator on the interwebs and see what the owners manual says . Out of curiosity , what's the motor do ? Just sit there and run or does it power something ?

Reply to
Terry Coombs

Thanks Terry,

It is only a 3-hole twist-lock socket on the generator. Looks like I will h ave to crank it up and get the meter out. I seem to recall using it to powe r something 220/240v about 6-years back, but no idea what wiring I used.

Reply to
Dave, I can't do that

If your gen ouit is 240, nor 120/240, the motor will connect across the 2 "line out" terminals while the third terminal will be a ground - no neutral.

If it is 120/240 it will have 4 wires unless it is ANCIENT

Reply to
Clare Snyder

The reason neutral wires are called that is because they are tied to ground in the breaker panel which means there is no potential voltage between the neutral wire and the ground wire, at least in the breaker panel. So there is no neutral on the generator unless it is tied to the generator ground and the generator is grounded. I'm betting that one wire is ground and that neither of the other two wires are tied to ground, meaning that there is no neutral wire on the 240 volt output. So you really need to get out the meter and see what the 240 out really is. Eric

Reply to
etpm

...

"The reason neutral wires are called that is because they are tied to ground" seems to me to be incorrect. True, in US wiring, neutral wires usually have near-ground voltages on them, but more generally a neutral wire is one with no current flowing in it when a system is in balance.

Reply to
James Waldby

Three wires is a common generator output. You will find that you have

110 - 0 - 110 volts. Just the same that feeds into a breaker box. The fourth wire that you need is ground. On 99.9% of generators you will find a ground lug on the generator head or near the output panel. That goes to a good ground.
Reply to
Steve W.

Generator grounding isn't obvious because it interacts with other considerations, for instance checking for buried utility lines before driving a ground rod, or impenetrable frozen soil.

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Neutral is the power return conductor. Ground is for safety, only carries fault current, and is connected (bonded) to Neutral only at the main breaker box, or the generator frame when it is an isolated, "separately derived" power source.

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"In other words, a ground rod is not required and, in fact, may create a hazard."

Naval standards don't ground the neutral so that a single short won't take down the ship's power. The problem with grid power is that the pole transformer secondary could short to the 19.9KV distribution line and bring high voltage into your house if you didn't have a ground rod connected to the neutral. That isn't an issue for generators.

Reply to
Jim Wilkins

In US wiring the neutral does have current running through it. Eric

Reply to
etpm

so I corrected your statement .

Reply to
Terry Coombs

The neutral is the center tap of the pole transformer, and the return for 120V loads. If you pull 50A from one hot leg and 40A from the other, the 10A difference will flow back on the neutral.

A voltmeter tells you nothing about currents, you need a clamp-on ammeter to measure them.

Reply to
Jim Wilkins

The neutral carries the difference between the hot leg currents. If the load current is 100A on one leg and 0A on the other the neutral will carry 100A. Increasing the load on the other leg decreases the current in the neutral, so with 100A through both hot legs the neutral carries 0A, not 200A, and it can be the same size cable as the two hots.

Conceptually you get the right answer if you treat both loops of the circuit as separate and then add the currents, If the neutral has 100A flowing in from one hot leg and simultaneously 100A out to the other they will sum to 0

The relevant circuit analysis principle is that the currents into and out of a wire junction have to sum to zero, since you can't create or destroy electrons. A capacitor at the junction doesn't negate this rule, it turns the solution into a problem in differential calculus whose answer is an equation of voltage versus time.

The Romans used the same net-sum principle to run an empire-wide checking system. When a merchant wrote a check for a cargo of wheat in Egypt the amount was simply deducted from tax payments sent back to Rome, and when he returned home the merchant had to reimburse the treasury (or become lion poop). Thus only the heavily guarded tax shipments were at risk from storms or pirates.

-jsw

Reply to
Jim Wilkins

in a properly balanced load center neutral current will vary , but the idea is to minimize it .

Reply to
Terry Coombs

The ship designers can predict and apportion the loads, which may not be practical for residential, commercial or industrial installations subject to unexpected, unengineered and perhaps undocumented changes. Plus warships are necessarily relatively symmetrical and redundant and lack the enormous motor startup surge capacity of the grid. The analysis I gave works for all situations, not just your well-designed and controlled ones.

I've traced and numbered my home outlets so I know which side, odd or even, they are all on. But I have to plug the portable air compressor and MIG, microwave, window air conditioners and heat treating oven into whichever hot leg's outlet is nearby. The 120V heating and cooling loads will never be balanced because they cycle randomly. I have a 200A electric heat service so balancing

Reply to
Jim Wilkins

and I'm trying to apportion loads to minimize neutral leg current . Just seems like the right way to do it - though I can see why a pro wiring a new house probably just sticks 'em wherever with no regard to balancing loads .

Reply to
Terry Coombs

Not when the circuit is ballanced

Reply to
Clare Snyder

I think balancing the loads is a good idea too, but I wouldn't let it override other standards.

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Reply to
Jim Wilkins

In the UK and Europe the neutral takes the same current as the live in

pulling current from one side of the centre tapped transformer.

Reply to
David Billington

True but irrelevant. When you drill a hole do you turn on a grinder to balance the demand?

Reply to
Jim Wilkins

Our hots and neutrals are the same gauge and as I pointed out the neutral current can't be more than the greater of the hot currents; the other 180-out 'phase' can only reduce it. Any imbalance doesn't feed back beyond the pole or distribution transformer which has a single 'phase' primary, so I don't see a significant problem as long as the currents stay within the wire, breaker and transformer ratings.

Three phase imbalance does feed back into the grid.

I tried to roughly balance them in the industrial equipment I designed because I had no idea what else might be on the circuits, then or later. However the control circuit was all on the same breaker pole and usually there wasn't anything comparable to put on the other one(s).

-jsw

Reply to
Jim Wilkins

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