- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
If I were to wire an office and it had all electronic ballast should I be concerned about using MWBC on these circuits? I assume electronic ballast are non linear-- Is that correct?
Electronic ballasts & non linear loads
- Thread starter Dennis Alwon
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
So you are saying there is no reason to be concerned with a MWBC serving fluorescent lighting with electronic ballasts.
I'd be wary of doing MWBC with electronic ballasts..even though the percentage isn't bad enough to affect load calcs that much harmonic distortion would be bad..remember depending upon each ballast's THD, they may add, subtract and multiply at random. Which could cause wire heating and more likely ballast failures.
Bid a bit more to cover the extra copper costs and avoid a lot of callbacks to change ballasts.
Bid a bit more to cover the extra copper costs and avoid a lot of callbacks to change ballasts.
If you are concerned about overloading the neutral, I don't think that is an issue at all. I would rather see MWBC's on lighting circuits than receptacle loads. With receptacles I'm always concerned about loosing the neutral, and having the receptacle voltage get to high.
With most modern multivolt ballasts, the ballast wouldn't even care if the voltage floated up to 240 volts.
I think there is probably a lot more "efficiency" benefit from using MWBC's on lighting loads, since the lights are often left on all day and Lower voltage drop = less energy wasted.
Steve
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Thank you both for your replies. This is not a job that I am doing. A fellow EC called me and asked-- I thought it would be fine but wasn't sure with electronic ballast.
Interestingly, the EC told me that someone said that they make 12/4 MC with a #10 neutral for this purpose. Had never seen that or heard of it.
Interestingly, the EC told me that someone said that they make 12/4 MC with a #10 neutral for this purpose. Had never seen that or heard of it.
MIEngineer
Member
- Location
- Michigan
I don't mean to hijack the thread, but here goes..... Why would a MWBC result in lower voltage drop at the load?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Please feel free to question -- I would never consider that hijacking a thread-- little offshoots perhaps but it is fine with me...:smile:
SmithBuilt
Senior Member
- Location
- Foothills of NC
I will give this a shot. Others will be along to correct me.
Assume the loads are balance on two (240V 1ph) or three phases. The neutral would theoretically not be needed. Therefore less resistance in the circuit.
weressl
Esteemed Member
If there is no return current the resistance does not matter. If it does not return via the neutral it still has to return tto the 'other' phase so it will contribute to the voltage drop through the path it takes.
There is no free lunch, what goes up must come down and all energy is already created in the Universe it just keep converting from one form to another, and so on and so forthings.......:grin:
- Location
- Massachusetts
Dennis every office and retail store i have ever wired used as many MWBCs as possible for the lighting.
I'd be wary of doing MWBC with electronic ballasts..even though the percentage isn't bad enough to affect load calcs that much harmonic distortion would be bad..remember depending upon each ballast's THD, they may add, subtract and multiply at random. Which could cause wire heating and more likely ballast failures.
Bid a bit more to cover the extra copper costs and avoid a lot of callbacks to change ballasts.
First there is no reason that MWBCs will cause ballast failures, none. (excluding open neutals)
Second lets be honest, you do not like MWBCs at all for any use.
I will take the semi free lunch and enjoy it.
From a long ago thread
Here is an illustration from Ed MacLarren that will help visualisation.
Roger
Less copper, less voltage drop sounds like a good thing to me.
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Lcdrwalker
Senior Member
- Location
- Columbus, Ohio
I always use MWBCs for lighting whenever possible.There is less of a voltage drop on longer circuits and there are less condutors that figure into possible derating.
- Location
- Massachusetts
In my area MC is king. We can get MC in all sorts of sizes and combination.
We would call that 12/4 '12/4 with a super neutral'. I have never seen it used for lighting but we have used miles of it for supplying office cubes.
We also get 12/8 or 10/8 MC cable. That contains black, red, blue, white twice and ground, sometime with a green with yellow for IGs. We use the 12/8 or 10/8 for homeruns from the panels out to central locations and then split out from that point.
Check out this catalog for tons of MC
http://www.afcweb.com/pdfs/afc_cable_catalog/AFC0706_Cbl Cat_pt1.pdf
You want some 10/16? They got it and at only 995 lbs per thousand.
SmithBuilt
Senior Member
- Location
- Foothills of NC
Bob I searched and searched to find that diagram. Would it be worth while to make that a sticky in the FAQ's? Or maybe a thread that explains it clearly, which probably does not exist.
I don't know much about the tags maybe it could be tagged for searching.
I don't know much about the tags maybe it could be tagged for searching.
peter d
Senior Member
- Location
- New England
And in the unlikely event that you can't find something you need, AFC will custom make it for you (with a minimum order of course.)
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
I believe that if you compared the THD of an older magnetic ballast to the newer electronic ballast, the magnetic ballast was equal or higher in many cases.
glene77is
Senior Member
- Location
- Memphis, TN
iwire said:
LOL I knew you'd say something to this. so I'll respond.
To the first, I respectfully disagree with the statement of "none", as it would depend on if the ballast itself was sensitive to harmonics. If so, there is a possibility of untimely failures due to the interacting harmonics.
In hindsight, it seems that such failures would be unlikely as ballast design should take into account multiple ballasts on one circuit, with MWBC's being a common practice. And I'm sure that actual real-world experience would bear that out.
I am pointing out the possibility of problems only.
To the second, I had to laugh as you and I have had this debate on another forum..remember I did concede that I have no problem with use of MWBC for lighting and other commercial applications, but in my current line of work they are verboten by design practice (mine and several other technicians in my field), manufacturer specs (AMX, Crestron and Vantage Lighting), and by actual, documented issues with sound system problems.
It's all a matter of application and experience really.
By the way, thanks for posting the diagrams on post #11, that is quite educational and a great find!!
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- Location
- Massachusetts
I will stick with 'none' as all equipment is supplied by a multi wire feeder with a common neutral for all loads. Unless your being supplied by a very unusual source.
That is one of many from Ed MacLarren, a member who I miss quite a bit, he was an instructor and a nice guy.
SmithBuilt
Senior Member
- Location
- Foothills of NC
How does that differ from what I said?
- Status