Current on a 12 gauge wire

[KennyG]

That's a clear way of stating it.

My question was, what if you wire 4 GFI's on one 12/3 MWBC, alternating them as you go, black leg, red leg, black leg, red leg, wired by the line terminals only, sharing the neutral as you go? Would that work?

Yes, it will work fine. I have that configuration in my pole barn/shop. The downside is that you pay extra for more GFIs, offsetting the saving in wire and complexity but on the plus side, you only lose one outlet if a GFI trips.

 

[LD1]

That's a clear way of stating it.

My question was, what if you wire 4 GFI's on one 12/3 MWBC, alternating them as you go, black leg, red leg, black leg, red leg, wired by the line terminals only, sharing the neutral as you go? Would that work?

Yep. Share the neutrals with whatever you want on the line side of the GFI.

The GFI only senses current on the load side. And a difference of more than 5ma between hot and neutral (on the load side) will trip it.

Load side can be either the load side screws that feed further outlets to be protected by the GFI (no neutral sharing off load side). Or it can be whatever is plugged into the GFI. Those are the two options for load.

Line side, do what you will.

 

[buickanddeere]

That's a clear way of stating it.

My question was, what if you wire 4 GFI's on one 12/3 MWBC, alternating them as you go, black leg, red leg, black leg, red leg, wired by the line terminals only, sharing the neutral as you go? Would that work?

What ?

 

[ray66v]

Thanks guys.

I didn't put any GFI's in my shop. They probably wouldn't work well. I had to put in hy-mag breakers, because some of my bigger 120v saws and grinders, can trip the standard 20 amp QO breakers on start up.

I'll put the GFI's in, when it's time to sell.

 

[ultrarunner]

If have GFCI's in the rentals but never in a home where I have lived... they were all older and predate GFCI and some predate grounding as in original 1922 service.

GFCI certainly have been the cause of service calls for the rentals... almost always it has been a tenant plugged in appliance but several times over the years I have had to replace the GFCI...

I also have a fair number of Hospital Grade GFCI at the Hospital... now over 20 years old and never an issue... they are all Hubble and were expensive even 20 years ago...

 

[Zerk]

We are building a home in the country and there are no building inspections or code requirements in this area. I?

Still bound by NEC. Just no local codes. Some counties or cities will be stricter than NEC. Which to me is BS. I am surpised being in TX you don't, they seem to like laws down there.

Less chance for problems if every circuit has it's own neutral. No shared neutral circuits. BTW, almost all circuits are designed to run at 80% max current. 15 amp breaker = 12 amps, 20 amp breaker = 16 amps.

Sort of. You derate for continuous loads. But that is a good rule of thumb.


Neutral sharing is not done as much anymore maybe, but nothing really wrong with it, if done by code. Think about a sub panel. That is one big shared neutral. I could see pull 12-3 to 4 pole with one 240 load, depending on the loads. I'd probably got to 10-3 though, but again depends on loads.



I would have the electrician explain if you are uncomfortable. Problem is you may be a big PIA, if you never understand it no matter how he explains it. Some people can't with electricty. They get all sketchy with details, than come on internet and it gets worse.

 

[Zerk]

If he's running (2) of the 12/3 wires you are good number of circuit wise, but I wouldn't let them do it in my house.

Why not?

 

[Zerk]

The water heater needs a 30 amp circuit on 10 gauge wire. That's 8 circuits for a modern kitchen.

Water heaters come in different size. This is why it is scary having people on the Internet give advice. You should not.

To do load calcs you work in watts. Then size wire and breakers.

A small water heater goes on 20 typically.


Also 8 circuits for a modern kitchen is silly.

 

[Zerk]

Six pages and I have read everyone of them :shocked: Lots of good information here though

we most be reading different threads.

 

[Zerk]

Great.

My first house, the power company used AL underground, from the transformer to the meter. I was lucky enough they used reasonable care when they did it. So, it never failed for the 23 years I was there either.

I'm not using it.

A great deal of wiring is aluminum. It is not used in branch circuits in home any more, except for ranges or sub panels. Massive amounts of aluminum are used else where.


Typically you increase by one wire size when running alum, instead of copper. You also put a coating under the lugs in the panel so they don't oxidize.


On one hand I say the codes get to crazy, on the other hand, I don't most people should do wiring, or talk about wiring.

 

[Zerk]

This is why refrigerator/ freezers are supposed to be on a dedicated circuit. Don't let a $10 appliance ruin a $1000 worth of food because of a tripped circuit.

Good advice, but not the end of the world if it not. when I recircuited existing home, I took micro wave and coffee pot off fridge circuit.


Again good advice, but not from God's mouth to your ear either. Plenty of homes have other stuff on, fridge circuit.

People should clamp the load in their house, you would be surprised how small it really is.

 

[Zerk]

Since I am always working with 3 phase circuits, I never trust a neutral. I wire things so the homeowner has to go out of their way to get in trouble.

Curious, around here most home owners do not have 3 phase. Apartments might have it, some farms. But it is very rare for a home to be 3 phase. Guy would have to have a shop of some kind.

 

[Zerk]

I was wiring y new house and asked an industrial electrician if I would be better off running 12 ga for lights instead of 14 ga for lights. He reached into his pocket and feigned throwing money on the ground. I got the picture. 14 ga. for lighting circuits after that.

I agree. I don't waste money on 12 ga for lights.

There was an ad in a magazine that tried selling bigger wire, less reistance, as a cost savings. I really doubt that was true, unless in some massive industrial situation. even then doubt it.

 

[Zerk]

(2) 12/3 Romex wires is up to 4 circuits. A kitchen would typically have a dedicated DW circuit, and 2 circuits for the plugs (maybe one on the island and the other on the other cabinets). I'm guessing (if it's not what is noted below) he ran (1) 12/3 for the DW and plugs and the second is either for other plugs and the WH or the WH is a little 240v.

Note- usually the DW is next to the sink. The sink usually has a disposer. It is very common to run a 14/3 or 12/3 for the DW and disposer. You just break the little bar that provides power between the top and bottom of the plug.

If the electrician does it for a living every day I'd bet a few bucks the 12/3 makes it back to the panel. The odds he ran out of wire and or did something else are slim. One possibility would be a junction box that was placed before the slab was poured. He can add the breaker tie later if it doesn't make it in. Why would the breakers be in before the plugs and switches are set anyway? Are they really all in?

I'm sure it will work fine. The fact that you didn't understand about the shared neutral has me thinking you are looking at stuff you don't fully understand. With that, you have worried yourself into thinking the worst. You hired the contractor after much research because you trust him and like him. Continue to do so!

It would be illegal to install a 30 amp dryer circuit in my city with 10 Gauge wire as code requires 8 Gauge...

That is limited to few areas. I dunno if wire company bribed city, or you got people that don't know electrical making laws. Some people seem to think NEC is on the ragged edge of safety and they know better, and will go a step further.

If you don't know what a handle tie is (or to ask what it is for) you shouldn't be taking the cover off of the panel box...

One of the better posts in this thread.

Aaron Z

The cable tie goes on the handle of the breaker. Same place you would reset a breaker. Not really taking cover off. A home owner with no knowledge is safe to do this

 

[GregbkH]

Massive amounts of aluminum are used else where.


Typically you increase by one wire size when running copper. You also put a coating under the lugs in the panel so they don't oxidize.


On one hand I say the codes get to crazy, on the other hand, I don't most people should do wiring, or talk about wiring.

Hopefully that is a typo. Usually you increase one wire size when running aluminum.

Typo's can be dangerous when talking about wiring.

 

[Oldoak]

Hopefully that is a typo. Usually you increase one wire size when running aluminum.

Typo's can be dangerous when talking about wiring.

And an anti-oxidant such as GB's Ox-Guard is used on aluminum wire connections.

 

[Zerk]

Hopefully that is a typo. Usually you increase one wire size when running aluminum.

Typo's can be dangerous when talking about wiring.

Yes one wires size over copper when using aluminum, my mistake. But should not be a big deal. You look it up in code or quick reference it will have all laid out for you.


You really shouldn't be getting conductor size from forum threads. Look it up.

 

[Zerk]

This is "Edison" circuit wiring with a shared neutral. .

This must be a regional term. Just sharing a neutral, is all I have ever heard.

 

[Zerk]

Thanks. So it sounds like the electrician is running a 20 amp, 240 v circuit to the island and splitting the legs there. I'll verify that he's using a full size 2 pole breaker. However, There are still 3 things that draw 1500 watts (12.5 amps), so he's got to be putting 2 of them on the same leg for a total of 25 amps on a 20 amp leg. That's a 125% load and according to the circuit breaker trip curves http://http://static.schneider-electric.us/docs/Circuit%20Protection/Molded%20Case%20Circuit%20Breakers/0100-400%20A%20Frame%20FA-LA/FA-FC-FH/0600DB0105.pdf (page 2) , that is in the manufacturing tolerance window of 2 to 3 minutes up to 2 or 3 hours before it trips. It does not seem like a good idea to me, but I can now see why he says it will work - he's hoping one of those 1500 watt items will turn off before it trips the breaker.

You hired the guy to do a job.


Not saying you shouldn't keep an eye on things, but unless you know what you are talking just making fuss.


Lots of things could be done. The wires don't even have to be on the same breaker. He could have one 240 V load, than wouldn't need the neutral sharing. He could have 2 120 loads, shared neutral. He could do a local disconnect and 4 circuit panel, doubt it, but could do it. He could use 4 circuit panel, and create 1 240 and 2 120 circuits.

How many watts is a 2 gallon water heater, 120 or 240? Dishwasher 120 or 240? Is the 2 gallon water heater part of the dishwasher, or just some point of use heater?


If he does use a 240 breaker, each leg is 20 amps. I am not sure you realize this. This is why work in watts not amps. Also you derate 125% for continuous loads, I am not sure if a dishwasher qualifies, because it goes through cycles. I may be wrong. But not everything is sized at 80% of capcity of the wire.


I get the impression you don't have a clue what is going on, and are just working yourself into a tizzy, along with other folks.

 

[Zerk]

BTW, almost all circuits are designed to run at 80% max current. 15 amp breaker = 12 amps, 20 amp breaker = 16 amps.

No. Somewhere people learned a small but of information, but not how to use it.

Continuous load, is for 3 hours. Thae derate.