Explaining MultiWire Circuits- For Fun :)

[Paul W. Abernathy]

No problem my Brother.......I knew what you were talking about....

[Paul W. Abernathy]

Ok...for those wanting to know what RMS is here you go.....lol....

rms: This is the root mean square value of an alternating current or voltage. It is the value generally displayed by an analog or digital electrical meter. For a sinusodial current or voltage the rms value is 0.707 times the zero to peak value of the sine wave. For a square wave current, the rms value is the same as the peak value.

Oh lets truly not discuss RMS...lol.......I can hear HEADS popping now...

[Russel Ray]

Originally Posted by pabernathy

RMS

Really Mean & Stupid

[mmorgan]

I inspected a house a couple of years ago where they tried to use this multi circuit technique (called "shared-neutral" down here). They made one serious error, however. They used a two-wire system (black, white and ground). They used the black on one circuit, the white on another circuit, but they used the bare ground as the neutral. I couldn't believe what I was seeing - and the entire house was done this way.

The deal fell through when they called in an electrician who confirmed what I had said and told them that the whole house needed to be rewired.



Mike

[Greg Fretwell]

Paul you may have a local AHJ who makes up a rule now and then but a multiwire circuit to a shed is one circuit in most of the US. No grounding electrode required. The GFCI only applies to the receptacle outlets so it can be accomplished in thew first ouitlet on the circuit once it hits the shed. That does mean you need the non-gfci burial depth.

[Paul W. Abernathy]

Greg,

I hear ya......But on more than (1) situation and by a rather WELL known electrical inspector in our area.....the running of a single 20A line to a shed from a 12/3 w/ g prompted the AHJ to force a panel at the shed and it's own GEC and GE because his classification was the 12/3 was not being used for 240V and was a 120V circuit and used as (2) circuits...thus rejected.

[Paul W. Abernathy]

Greg,

Here is where I think they get messed up.......when trying to relavate Art 225.30 and 250.32(A) Exception together....

Personally I don't have a problem with a Multi-Wire circuit to a shed IF in know whats going in it and how it is being wired...otherwise if they are going through the trouble to take 3 wire w/g anyway I would prefer them to size it up ( if able to do so ) and place a 4 ckt panel in the shed....and ground it and treat it as a normal detached building....but thats me...

Another big issue I believe is they try to bring in Art 225.32 into the mix and just plain want a disconnection means.....my honest opinion.

again was me just giving an example of something local I see....personally again all the sheds I see and wire get a panel in them with available 240V 's...

[Paul W. Abernathy]

Russel..........WHAT.....lol.......Thats not my verbage on RMS...lol......thats my verbage on my wife when she is on PMS....

[Bob Badger]

Paul per the NEC definition a multiwire branch circuit is one circuit.

Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.

Also notice that the definition is not called branch circuits multiwire.

[Paul W. Abernathy]

lol....Bobster......First..Great to have you back.....Second......I did not debate the single circuit...lol.....Was only saying what I witnessed from the local AHJ on his idea of the (2) circuits concept....

Man.....Bob......Go back and read the first post fella........GOD its great to have ya back...thehehehehehe

[Paul W. Abernathy]

man I was not talking about the multiwire per say in that I was saying...lol....What I was saying was an an example of where a local well known AHJ ruled it was (2) circuits because of how it was done at the shed and made the guy do a panel and GEC and GE because of it.....

I know....I heard his whining and inspected the shed a year later.......and asked the local AHJ about it...and a year later he told me the same thing...( he was on another job my company was doing so I asked him..no harm no foul...lol )

Actually.....I am seeing the guy again on Friday I think....I will ask him again because I did tell him it was a single circuit per the NEC and he looked at me and smiled.......but again that was some time ago so it might be fun to CRACK the ice with him again......AFTER he inspects the project of course...thehehehehhee

I dont need him to fail a job out of spite...lol.......

Actually the topic was explaining multiwire circuits as a general....explaining ALL multi-wire circuits...circuits being the plural for all...lol.....in general speaking terms....Dang I need one of those RRAY martini's now....

I tried to make an attempt to take it deeper to the allowance of (1) branch circuit to a building that in doing so did not need a seperate GE at the building...and at what point ( even in the local AHJ's ) eyes it becomes (2) circuits......the reason I bought it up is it came to mind my conversation with the guy....lol.....so I figured hell let me add it...lol

[Bob Badger]

Paul I was just giving you some ammo to shoot the AHJ with.

The AHJ is wrong to force a panel and or electrode installed if the shed is fed with one multiwire branch circuit.

[Bob Badger]

By the way thanks for the welcome.

[Paul W. Abernathy]

Bob,

I hear ya brother...Actually I could not give him too much greif over it as I only saw it and heard the story because the guy was selling the house and shed and I was doing an inspection on it and saw the signature of the inspector.

I told the guy it did not need the panel and so on and he started...the inspector this....and that so I just happen to run into that inspector ( who is a great guy BTW ) at one of my job sites a few days later and asked him about it and thats where the conversation started...lol....but heck it was a year or so ago now...

I told him the same thing as it was a single circuit but he insisted it was considered (2) because of the nature of the layout and what the guy was trying to do....but HELL I am not going to argue as I would not have wired it that way personally....and most certainly did not want him to reject the project we did since he has not inspected it yet...lol......he passed ours but thats where I left it...lol....

I think I will not bring it up to him again on friday since to be honest with you I think that house and shed was sold over a year ago...lol....the guy who was whinning has moved on I am sure...lol...

Just thought it was a neat story.........But I get into trouble on here when I bring stories to the mix....lol.....I will TRY real hard to not bring up stories again...theheheheh

[Greg Sullivan]

I've been following this thread with great interest. I'm not an electrical engineer, but I've had a fair amount of experience working with single phase power. I'm hoping one of you can clarify something for me.

Example: When a dryer is connected to 220 VAC, it is called single phase 220. If I use a volt meter and measure across phase A and phase B of a 3 phase outlet, it will read 220 VAC. Each phase will show 120 volts to ground. Phase A and B are shifted by 120 degrees. Is the power going to the dryer made up from two of the three phases (legs?) or is the power to the dryer actually one phase that is somehow shifted by 180 degrees? I hope this question makes sense.

I've seen many references to 180 degree shift and 120 degree shift. I was not aware of the 180 degree shift. How is the 180 degree shift produced? I know that three phase power is what the generating station is supplying and each phase is shifted by 120 degrees. It's the 180 degrees that has me confused.

Thanks in advance,
Greg Sullivan / Canyon Lake, CA.