New Tank Circuit Added

[AlanM]

Nice, thanks.

[YHSublime]

Thanks Mods for splitting....did not mean to hyjack the other thread.

This is more interesting than the other one anyway...

 

Well now I'm gonna hijack this one!

 

Just kidding.

 

No faith in pops?!?! Hope he doesn't find out about this thread...okay, I am convinced this is good, next topic...

 

John, do you think you might have attention deficit di... hey! Lets go look at aquariums!

 

hmmm this might be the best part of this whole thread....let's talk beer fridges

 

Now we're talking!

[Origami]

Educational thread. Thanks. I would have been concerned about the potentially higher current (>30 Amps)on the bonded return, but those in the profession are not. You learn something every day. Good stuff to know.

[linkfalcon]

Lots of good info here

[Coral Hind]

Educational thread. Thanks. I would have been concerned about the potentially higher current (>30 Amps)on the bonded return, but those in the profession are not. You learn something every day. Good stuff to know.

The shared neutral or "Edison Circuit" works differently because each leg is 180 degrees out of phase from each other. That means the two hot wires will roughly balance out the returning current on the neutral. So, if both legs draw equally 10A, then the return current on the neutral will be zero. If phase 1 draws 5A and phase 2 draws 10A then the difference of 5A will flow back on the neutral. It is really no different than the main panel which only has one neutral going back to the transformer.

 

When running the shared neutrals as his dad did there are certain things you have to make sure of:

 

1. The two hots need to be from seperate phases!! If you pulled it from two 20A breaks on the same phase then you could have up to 40A on the shared neutral. I'll say it again, they must be from different phases. Normally if the breakers are next to each other, not the tandem types, then they are on different phases. Using a double pole breaker ensures that seperate phase use as well as item #2 below.

 

2. The two breakers' handles must be bonded to have a common trip so if one trips it also trips out the other breaker. This is a newer NEC requirement as of 2008 so Steve your father might not know about that. Adding a simple metal tie bar will fix that requirement.

[STEVE]

Thanks Dave...I will bring it to his attention when he gets back in town.

[AlanM]

I thought the point of a tandem (piggyback) breaker was that you could get two circuits from one slot in the box, which would mean that the two hots would be on the same phase. At least that's how I understood that these worked:

 

http://www.lowes.com...oductId=1111749

 

How would you get them on different phases? Would you put the tandem breaker in and then move an adjacent hot to one side of the tandem breaker and wire your new circuit with the red and black split between the old breaker and the other side of the new tandem one? I guess that would get them on different phases. You just couldn't put the new black and red both on the same tandem breaker.

 

1. The two hots need to be from seperate phases!! If you pulled it from two 20A breaks on the same phase then you could have up to 40A on the shared neutral. Ill say it again, they must be from different phases. Normally if the breakers are next to each other then they are on different phases and using a double pole breaker ensures that, as well as item #2 below.

 

Also, my box needs a new tank circuit too, but the side with openings has a full neutral bus. The inside of the box is very organized at the moment with nothing crossing the mid-plane when it comes in the top. Is it OK to put a neutral and ground coming in to the left side if the breaker and the hot is coming to the right?

Edited March 29, 2013 by AlanM

[Coral Hind]

Tandem or pancack breaker, the term piggyback is confusing when used here. Tandem breakers are totally fine to use but I think you are confused by the shared neutral discussion above. If you are going to use a tandem breaker to pull power from one phase then they have to have individual neutrals for each switch of the breaker. So, two hots going out with two neutrals coming back. You could not use a 12/3 as Steve's dad did but instead use two seperate 12/2 cables. If you tried a shared neutral with the tandem breaker you would not get the out of phase cancelling but instead get an addition of the two switches on the tandem breaker coming back on the one neutral. Sharing neutrals only works when the hots are out of phase from each other to cancel each other out.

 

It is fine to run the wires to the other side of the panel to put them on the correct bar.

[paul b]

Coral Hind, you said in 2008 they changed the code so that the 2 breakers that share the same neutral must be connected?

I was a commercial master electrician in Manhattan and I retired after 40 years in 2008 so that may be true and interesting. It was always a violation to connect the breakers together unless you were running a 220 load.

 

Almost all circuits on all loads use shared neutrals, and in commercial applications which are 3 phase panels, three circuits share the same neutral. It's just cheaper to wire like that because copper is so expensive. So does the new code extend to 3 phase commercial panels as well?

[Coral Hind]

Paul,

 

In 2008 they added to 210.4(b): "Each multi-wire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point of origin."

It was a safety factor so service electricians would not be working on a circuit they assumed was off but had a neutral that was carrying voltage from another breaker.

 

They also limited the number of shared neutrals allowed in a system so you are really limited. Article 215.4(a), "Feeders with Common Neutral. Up to three sets of 3-wire feeders or two sets of 4-wire or 5-wire feeders shall be permitted to utilize a common neutral" SO it's still allowed for commerical, just limited.

[AlanM]

BTW, if every new breaker installed for general outlets ends up needing to be AFCI since 2008 NEC I hope they are putting in really tall boxes because those AFCI ones make it impossible to put in breakers in both columns. Unless the new boxes are made much wider, I guess.

[paul b]

Coral Hind, thank God I retired and I don't have to remember that. Soon we will be so safe that we won't use electricity any more. Maybe we will use air instead.

Thank you for letting me know.