ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
Increasing demand factors in residential
by gfretwell - 03/28/24 12:43 AM
Portable generator question
by Steve Miller - 03/19/24 08:50 PM
Do we need grounding?
by NORCAL - 03/19/24 05:11 PM
240V only in a home and NEC?
by dsk - 03/19/24 06:33 AM
Cordless Tools: The Obvious Question
by renosteinke - 03/14/24 08:05 PM
New in the Gallery:
This is a new one
This is a new one
by timmp, September 24
Few pics I found
Few pics I found
by timmp, August 15
Who's Online Now
1 members (CoolWill), 250 guests, and 13 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Page 2 of 3 1 2 3
Joined: Oct 2004
Posts: 55
R
Member
I have often thought that it would be a good idea if the manufacturers of panels were required to put labels on the cover of the electrical panel that said something like "CAUTION modificcation or maitenance of this system other than by a qualified electrician may result in electric shock or fire and could void your homeowners policy." In a lot of cases it wouldn't do any good but for some it might make them think twice.
As far as a shared neutral, as long as the circuits are identified in all locations accessable then it would be a okay but I think it can become a problem when several branch circuits are in the same junction box. In most installations it isn't a problem but I have seen it in larger custom homes.

Joined: May 2004
Posts: 697
D
Member
I probably wouldn't object to multi-wire branch circuits if it were common to keep them together, and label, but all too often I'm doing a service upgrade and there is a conduit with five circuits and only three or four neutrals. I can either put the circuits on the same leg they came from in the new panel, or burn a few hours tracing wires.

In other cases it is a three wire romex or BX and it's obvious. I twist the wires together right up to the breakers where a non-professional will probably notice something is meant to be that way.

Dave

Joined: Mar 2002
Posts: 582
R
Ron Offline
Member
Considering that I don't do residential either, but a multiwire circuit would cause a harmonic issue in a residence with a 120/240 single phase service.
On the other hand, every project I work on in a commercial building (high tech type facilities), does not permit multiwire circuits due to harmonic loading.


Ron
Joined: Sep 2003
Posts: 650
W
Member
Three phase circuits have problems with triplen harmonics (the third harmonic and its odd multiples) because they do not balance on the neutral; instead they add up. All other harmonics will balance on the neutral if they are from a balanced source (eg. the 5th harmonic from a three phase rectifier).

The neutral in a residential single phase multiwire circuit does not have a problem with triplen harmonics; they balance just like any odd order harmonic. However in this case the neutral will have problems with even order harmonics.

With rectifier power supplies, even order harmonics are much lower intensity than odd order harmonics. You only see even order harmonics from the hysteresis of the load.

-Jon

Joined: Jan 2003
Posts: 4,391
I
Moderator
Ron I have always had a hard time understanding why moving the point the grounded conductor becomes also the common conductor would make a difference to power quality.

I understand the issue of overloading the common conductor by harmonic currents. That can be avoided by either not loading each leg of the circuit heavily or using a larger neutral conductor.

Assuming we have done one of the above, would there be any other power quality issues?

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Mar 2002
Posts: 582
R
Ron Offline
Member
Bob,
Yes, if you reduce the load on the phase conductors, or enlarge the neutral it will suffice. It doesn't remove or mitigate the harmonics, it just gives the circuit a fighting chance from the heat.
Most folks do not do either, so that is why I generally don't permit it.
By the time you get upto the larger switchboards/switchgear, it is not usually needed to enlarge the neutral, as the other loads (of different types) on that larger piece of the distribution system will have "diluted" the harmonic load into a larger capacity equipment.


Ron
Joined: Feb 2003
Posts: 687
A
Member
I too hate when the nutral is not marked with what hot it goes to. By adding a nutral for every circuit are you really making it simpler? It would seem to me that you are adding much more nutrals to get confused.

In the simplest form a residence if you had 2 hots and a nutral in a pipe there would be nothing to keep track of. Add another nutral and now you need to keep track of each one in each location. You want to worry about the homeowner? What's to say he will use the right one of those nutrals when he adds something. I don't think you can protect the HO from messing up the nutrals unless you keep it to only 2 wires per pipe.

It would be even worse of a mess when you have more than 2 circuits in a pipe. You can argue how many of what wire should go in a pipe. The reality is most HR in pipe have more than 4 circuits.

It is not just the cost of wire. Pipe costs a lot now. If you need to go to the next size up or more HR that costs $$. It seems to take a bit more labor for every size of pipe you go up. More labor in pulling, splicing, and keeping track of those extra nutrals. More wires you need to cram in a box or get bigger boxes.

I like what others have said about not tring to HO proof the instulation. If they wanted to do that they should sell tamper proof screws for any electrical cover or trim plate. Then only sell the removal tool to licenced EC.

Tom

Joined: Dec 2000
Posts: 4,294
Member
I think that a label is an easy, inexpensive way to provide an extra margin of safety.

Last week I hooked some machinery up. I connected the transformers as 240V 3Ø corner grounded deltas, which to some could be quite confusing. (the vendor's technician had never heard of such a thing, although it was his company that requested a grounded supply system).

Labels to identify this cost about 40 cents apiece, and took me less than 5 minutes to make.
Well worth the effort, I say.

As to a homeowner making modifications to his system, if we were to label all the possible misteaks they could make, there would be no room left for anything but labels.
I love residential multiwire branch circuits. 2 wire branch circuits just waste wire and create more heat. As Roger said above, there isn't any issue with power quality (harmonics) on a 1Ø 3Wire system...S


[This message has been edited by electure (edited 10-04-2004).]

Joined: Feb 2003
Posts: 24
D
Member
If your running multiwire circuits for everything. Then how are you wiring your ARC-FAULT BREAKERS in your bedrooms?

Joined: Jun 2004
Posts: 206
C
Member
Doug, Arc Fault breakers are available for multiwire circuits.

Page 2 of 3 1 2 3

Link Copied to Clipboard
Powered by UBB.threads™ PHP Forum Software 7.7.5