what is the case against daisy chaining fixtures?

M

malachi constant

Senior Member
Location
Minneapolis
Consulting engineer here. Been in the business since 2000 and every design firm I've worked at has "daisy chaining of fixtures not allowed" in the spec. I had assumed the reasoning was that interruption of one fixture would kill power to downstream fixtures though since fixtures should not be worked on live anyway this is less of an issue. Reading through this forum I wonder if back in the day daisy chaining was easy to get wrong / not a given it would be done legally if you didn't have a strong grasp of what was required. But now between code and manufacturing practices it is basically hard to do it wrong? As the engineer I'm not in tune to the means and methods of fixture whips and connectors and whatnot.

The context for me is in brick and mortar construction - schools, courts, hospitals, government facility office spaces... (not industrial, residential).

I consider this an opportunity to reexamine why we have we been doing things this way in the first place, and does it still make sense? Is daisy chaining a legacy best practice that no longer makes sense, or are there still good reasons for prohibiting it? I would appreciate your collective wisdom here!
 
IMO, "daisy chaining" fixtures is approved IF the conductors in the whip are sized appropriately.
On one job, I counted 9 fixtures "daisy chained" with what a #18 conductor. That doesn't work.

Ron
 
infinity said:
What's your definition of daisy chaining in this context?
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I'm with you on this. Lay in luminaires in ceiling grid - can be done but at same time sort of impractical or has other code issues if using the the typical 3/8 flex whips and 16 or 18 AWG conductors in it.

Back in the day when surface mounted linear fluorescent luminaires was a big thing, it was pretty standard to connect them end to end and continuous feed through them, including multiple circuits in the row in some cases. This still is allowed, just isn't as common of a luminaire type as it once was other than maybe when dealing with something existing at times.
 
kwired said:
Back in the day when surface mounted linear fluorescent luminaires was a big thing, it was pretty standard to connect them end to end and continuous feed through them, including multiple circuits in the row in some cases.
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I kind of remember the manufacturers limiting the number of fixtures that could be daisy chained to limit the amount of wire in the fixtures.

-Hal
 
hbiss said:
I kind of remember the manufacturers limiting the number of fixtures that could be daisy chained to limit the amount of wire in the fixtures.

-Hal
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Most them only had 1/2 KO's in them. The end plates weren't big enough to go any more than a 1" entry. Suppose you could get a 2.5" in from back side if you really wanted to, not sure how many luminaires that might been able to supply if you had that as full as code would allow :cool:
 
infinity said:
What's your definition of daisy chaining in this context?
Click to expand...
Typical example, a classroom with (12) lay-in 2x4s. We allow a whip connection direct from fixture to j-box. We have a max length allowed for the whip (I forget what it is) which effectively limits four fixtures per j-box. Every once in awhile a contractor asks if they can daisy chain. I assume that means one or two j-boxes, from which a whip goes to one fixture, and then from that fixture to the next, and so on. One contractor - a really good, trusted contractor - drew me up a diagram that proposed all twelve fixtures whipped in series (with the circuit snaking through the room) which I did not allow.

We don't do a lot of shell space / tenant fit outs - I can see why daisy chaining would be discouraged in that application.

With schools and offices there are a lot of long corridors, and over the years the facilities often add in double doors to break up the corridor for various reasons. I could see how it would be an unexpected cost if you wanted to break up the corridor lighting circuit and had to run a branch circuit 100'.

Our spec does not allow conductors smaller than #12. I've always assumed that was what was used for contractor-supplied fixture whips but don't know for sure.

Maybe in a mid-size room such as a classroom this is something reasonable to allow? I'm just not sure what I would and wouldn't want to allow, and then how to craft a master spec that is clear but flexible...
 
malachi constant said:
One contractor - a really good, trusted contractor - drew me up a diagram that proposed all twelve fixtures whipped in series (with the circuit snaking through the room) which I did not allow.
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That is fine (code wise) as long as the conductors in the whip are the same size as the branch circuit conductors.
malachi constant said:
I've always assumed that was what was used for contractor-supplied fixture whips but don't know for sure.
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Typical fixture whips use 16 or 18 AWG fixture wire.
 
kwired said:
Most them only had 1/2 KO's in them. The end plates weren't big enough to go any more than a 1" entry. Suppose you could get a 2.5" in from back side if you really wanted to, not sure how many luminaires that might been able to supply if you had that as full as code would allow :cool:
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I dont think you can use light fixtures as raceways unless they are listed as such and then only for the circuits involved.....
I've been wrong before.....:giggle:
 
spacing in a cassroom will be different than corridor spacing.
More important.. are you talking series? Or parrallel?
Anyhow, you arw still "daisy chaining" j-boxes... 2×4 lay in whips are rarely long enough to "daisy chain" together...
 
malachi constant said:
Every once in awhile a contractor asks if they can daisy chain. I assume that means one or two j-boxes, from which a whip goes to one fixture, and then from that fixture to the next, and so on.
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Pretty standard to do this with MC cable especially when you have a non-accessible ceiling type.
 
qcroanoke said:
I dont think you can use light fixtures as raceways unless they are listed as such and then only for the circuits involved.....
I've been wrong before.....:giggle:
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I haven't dealt with this in some time, but from recollection yes they likely needed listed for such. Most if not all the old fluorescent strip fixtures were listed for such. Most them even were designed to assemble by installing the end plate in slots in two adjacent fixtures to make an open channel through all the fixtures in a row if they are all connected in this manner. From what I remember you could supply other fixtures on different circuits or other switches but pulling non lighting circuit conductors through the fixtures was not allowed. This kind of lighting fixture kind of has disappeared from new installations over the years. There are some LED strips that are similar design, but not too common for lighting say a retail floor or other large area anyway.
 
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