ECN Forum Forums General Topics of the Trade General Discussion Area Failed Inspection, need two pole breaker

LK I know you are an experienced electrician, but I do not think you realize how prevalent multiwire branch circuits are outside of dwelling units.


Can you explain how we are going to loose the building?

All services are essentially multiwire branch circuits.

There is a great savings in labor and material that gets passed on to the customer on a larger project, yes we do get jobs where the specs say each circuit to have it's own grounded conductor and for this the customer has to pay more.

You must think of the scale of the work, an office building may have 100 to 300 circuits per floor. Most with only 1 to 4 outlets on them or about 10 amps of 277 lighting.

What I am really trying to say is, it's all in what your used to doing and to each their own.

Take Care and we all care about safety or we would not spend our off time talking shop.

Bob

Bob,

Had many years in Commercial and High Rise work. It would take pages to tell you the problems with office cube wiring. It's the office furniture design of the older cubes that presented the problems. The heavy use of electronic equipment in these cubes, cause problems in the entire system. I worked for a number of years with power engineers, and the office furniture design engineers to resolve building system problems. Today when electrical distribution
for office use is designed, most but not all of the problems have been resolved. While talking about the contact hazards involved in multiwire circuits, system failure and fire is another hazard in the older cubes and building distribution equipment. What we found going on in the floor transformers, and distribution panel neutrals was something I had never considered, circulating currents, causing temp rise in the system. again it all depends on the design of the system. Good design up front less problems in the end.

[This message has been edited by LK (edited 09-20-2003).]

[This message has been edited by LK (edited 09-20-2003).]

Don's continuing reference to "multi wire branch circuit" goes a long way here.

Note he never said "circuits" this means one circuit.

A "multi wire circuit" may be considered more than one circuit but is recognized as one circuit.

With that said, any electrician should recognize a multi wire circuit in a box and would be red flagged by more than one ungrounded conductor in the presence of one grounded conductor.

All wiring downstream of the split would be a two wire circuit.

Roger

LK point taken and I am sorry I did not know your past background.

The way it is now we are running 200% neutrals and I think the term is "K rated" transformers. (or is that the shielded ones?)

I can see that when all these non-liner loads where introduced to the old building systems that could cause trouble.

Now with the furniture using a 10 white with 12 hots and many labeled for 15 amp OCP I do not see any problems with overloaded neutrals.

Bob

Bob,

Yes, they have improved the cube systems, and the K rated transformers help Q things up, however there are still plenty of those old cubes in use. Multiwire circuits are ok if, used for the right application.

Les

Get ready for it....

In Canada, it has been a rule since at least the '80s when I started the trade.

All circuits sharing a neutral, in residential, shall be two pole or have tie-bars.
I always assumed it was so when a non-electrician wanted to turn the power off, he did; 'to the whole JB'. It is only for residential, but I can see the point.