Yet another MWBC question.....pushing the limits........

[kwired]

Thank you. I'd pull 2 sets of B,O,Y,W/Gr. One set (boat) of spools on one rod, the other on a second. I dont think you can use red, black, blue if you have a 120/208 or 120/240 service also in the building

I looked up 100% breakers. SQD makes them, C suffix indicates the 100% use. Here is one such 277V 20A:

https://www.southlandelectrical.com/ItemDesc.asp?IC=FY14020C-NS

Mains and the like may be rated continuous, but most breakers are not. You'd have to spec them. They might not be available for your existing panel.

One other thing; for existing conduits, it's a good idea to blow em out before pulling in wire. A tank of compressed air is cheap, or just use an air compressor with the rubber tip on it.

The existing EMT, did it go to previous MH/HPS lights? If so, are the existing conductors still in place?

eta: All breakers can handle their listed ampacity. iow, if you calculate a 19.999A load, you can use a 20A breaker... or even a 20.4A load, since fractions less than 0.5 are ignored. However, if that load is expected to run 3 or more hours, you are limited to 80% of the breaker's capacity (16A for a 20A), unless you get a breaker designed for 100% loading.

If you wanted to get creative, you could run all your lights thru a timer that would let them run 2:59, cut off for one minute, then restart, avoiding the continuous load. You'd probably never get another lighting job ever again tho lol.

Where do you find that is a continuous rated breaker? The C suffix on the breaker you linked to means it connects to the "C" bus in the panel. You must designate which bus the breaker connects to with one and two pole I line breakers.

 

[JFletcher]

Where do you find that is a continuous rated breaker? The C suffix on the breaker you linked to means it connects to the "C" bus in the panel. You must designate which bus the breaker connects to with one and two pole I line breakers.

http://blog.schneider-electric.com/...g-confusion-80-vs-100-rated-circuit-breakers/

"In the circuit breaker world there’s been some misunderstanding about the terms “100%-rated” and “80%-rated” circuit breakers. To dispel the confusion, Schneider Electric’s Mohamed Shishani ...."

"Mohamed Shishani July 16th, 2014
@Mike Ahern, 100% breakers are identified with a “C” suffix in the part numbers in the online digest. For 100% rated circuit breakers add a “C” in the 9th character place (for example, HDL26015C or JDL26150C)"

Granted it's a blog and an unverified commentor.

The previous points about the panel and all other breakers needing 100% rating make a single 100% rated breaker (or even a few of them) a moot point, even if the above info is 100% correct.

eta: the breaker I linked has the C in the 8th place, not 9th. :slaphead:

 

[kwired]

http://blog.schneider-electric.com/...g-confusion-80-vs-100-rated-circuit-breakers/

"In the circuit breaker world there’s been some misunderstanding about the terms “100%-rated” and “80%-rated” circuit breakers. To dispel the confusion, Schneider Electric’s Mohamed Shishani ...."

"Mohamed Shishani July 16th, 2014
@Mike Ahern, 100% breakers are identified with a “C” suffix in the part numbers in the online digest. For 100% rated circuit breakers add a “C” in the 9th character place (for example, HDL26015C or JDL26150C)"

Granted it's a blog and an unverified commentor.

The previous points about the panel and all other breakers needing 100% rating make a single 100% rated breaker (or even a few of them) a moot point, even if the above info is 100% correct.

eta: the breaker I linked has the C in the 8th place, not 9th. :slaphead:

And to rub it in a little more if you ever ordered a single or two pole I line breaker you need to complete the catalog number with A,B or C, or two of those letters to designate which bus(es) the breaker connects to.

 

[dionysius]

I do not want to interrupt the fruitful discussion re breakers but I do want to add this note.

I met with customer today and he is willing to give up on his 1/2" conduit/Jbox reuse. Since he is expanding anyway (extra conduits to be run) he is accepting the argument (which is attributable to you super smart and super sharing folks) that new conduit should be run and to tear out the 1/2" stuff. Our job is electrical plus politics. Being confident about my information carries weight. I laud you folks for giving me some of that confidence because it is the truth.

My approach (based mostly on what this thread has stated) is to go with:

2 boats of #12 stranded in 3/4" EMT using 20A off the shelf common trip breakers yielding 36 lights per conduit run. ​

The pull is easier and a boat yields 18 lights which will fit his geometry very well.

His control choice is via Intermatic 3 pole 277V rated timers, so 1 timer per boat switching the hots. No neutral switching.

I cannot come up with a better solution.........what about it?????? And what about his timer choice????

 

[kwired]

I do not want to interrupt the fruitful discussion re breakers but I do want to add this note.

I met with customer today and he is willing to give up on his 1/2" conduit/Jbox reuse. Since he is expanding anyway (extra conduits to be run) he is accepting the argument (which is attributable to you super smart and super sharing folks) that new conduit should be run and to tear out the 1/2" stuff. Our job is electrical plus politics. Being confident about my information carries weight. I laud you folks for giving me some of that confidence because it is the truth.

My approach (based mostly on what this thread has stated) is to go with:

2 boats of #12 stranded in 3/4" EMT using 20A off the shelf common trip breakers yielding 36 lights per conduit run. ​

The pull is easier and a boat yields 18 lights which will fit his geometry very well.

His control choice is via Intermatic 3 pole 277V rated timers, so 1 timer per boat switching the hots. No neutral switching.

I cannot come up with a better solution.........what about it?????? And what about his timer choice????

May or may not be worth tearing out the old. 2 boats in 3/4" is probably the best option when starting from scratch. Instead of ripping out existing and starting over, adding a second 1/2 inch may make sense, or it may not. Only replacing a common "home run" portion of the existing may also make sense and then split off into 1/2 inch runs, some of them being existing.

 

[dionysius]

Summary to date plus a question........

Summary to date plus a question........

May or may not be worth tearing out the old. 2 boats in 3/4" is probably the best option when starting from scratch. Instead of ripping out existing and starting over, adding a second 1/2 inch may make sense, or it may not. Only replacing a common "home run" portion of the existing may also make sense and then split off into 1/2 inch runs, some of them being existing.

So here is where I am at for what I see as the optimal solution:?.........

-------------------------------------------------------------------------------------------------------------------
For each set of 36 650W 277V fixtures all from the same panelboard:​

1 3/4" EMT Conduit
8 CCCs #12 AWG stranded wire or 2 boats (A, B, C, plus N) per conduit (colors: Brown, Orange, Yellow, White)
2 common trip 20A 3 pole breakers
6 contiguous single pole breaker spaces used
2 Three pole 277V rated timers
Neutrals pigtailed at each light​

------------------------------------------------------------------------------------------------------------------------------------------​

I do have a question on which of the following facilitates the least labor/material approach for ground for each conduit??????

a. 2 Ground wires #12 (color: Green, 1 per boat)
b. Use the EMT
c. Any other more optimal choice​

​

 

[roger]

I do have a question on which of the following facilitates the least labor/material approach for ground for each conduit??????

a. 2 Ground wires #12 (color: Green, 1 per boat)
b. Use the EMT
c. Any other more optimal choice​

​

Read 250.118 and 250.122(C) then go with either one or both.

Roger

 

[kwired]

I do have a question on which of the following facilitates the least labor/material approach for ground for each conduit??????

a. 2 Ground wires #12 (color: Green, 1 per boat)
b. Use the EMT
c. Any other more optimal choice​

​

Least labor/material is to use the EMT as the EGC.

If you have other reasons to pull wire type EGC, only one per raceway is sufficient. If you pull more then one you need to connect them together at every splice/junction box anyway

 

[JFletcher]

So here is where I am at for what I see as the optimal solution:?.........

-------------------------------------------------------------------------------------------------------------------
For each set of 36 650W 277V fixtures all from the same panelboard:​

1 3/4" EMT Conduit
8 CCCs #12 AWG stranded wire or 2 boats (A, B, C, plus N) per conduit (colors: Brown, Orange, Yellow, White)
2 common trip 20A 3 pole breakers
6 contiguous single pole breaker spaces used
2 Three pole 277V rated timers
Neutrals pigtailed at each light​

------------------------------------------------------------------------------------------------------------------------------------------​

I do have a question on which of the following facilitates the least labor/material approach for ground for each conduit??????

a. 2 Ground wires #12 (color: Green, 1 per boat)
b. Use the EMT
c. Any other more optimal choice​

​

One ground per pipe. Three things not mentioned: what is the application of the lights (warehouse, gymnasium, parking lot/garage, etc) and how far/how many bends from the panel to the first light? Is any of the install in a wet location?

Tho you can use the EMT as the EGC, if there is any chance of the EMT being damaged (like a forklift in a warehouse), or you have to use FMC whips to the lights, I'd pull a #12 EGC. 9 #12s in a 1/2" conduit is right at 40% fill. I say 1/2" still since one conduit is already there, 1/2" is cheaper than 3/4", and if there are any appreciable # of bends that would have to be done by hand, 1/2" is easier to bend... tho 2 3/4" conduits would be easier to get 8/9 #12s (or larger wire to account for VD) thru, and more labor and materials = more $$$ for you.

Putting a pull box every 100-150' or per 2 90s will make getting 9 #12s into a half inch conduit much easier by hand. If using the light bodies as j-boxes would make the pull tough, put a j-box at/near every light then a whip from that to the light fixture.

Also, if you wind up hanging strut to support the EMT, make it wide enough to be able to run more conduits in the future w/o having to rework it.