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

[Smart $]

A quibble, but IMHO a significant one:

The neutral of a full boat, even with only linear loads, is still a CCC if the load is not perfectly balanced. It is just not counted as a CCC for derating purposes.

Yes, but we here "understand" CCC to mean a conductor counted as a current-carrying conductor. So do you want us to start using CCCC?

 

[GoldDigger]

Yes, but we here "understand" CCC to mean a conductor counted as a current-carrying conductor. So do you want us to start using CCCC?

That would be CCCCC not CCC. :angel:

 

[Electric-Light]

Many GSFL and LED ballasts are rated 120 to 277v. The active front end attempts to mirror the voltage waveform and you do get power factor over 0.98 and THD 10-20%. This gets you close enough to easily get wattage with an ammeter, but a close look of the current waveform would look like a sine wave drawn out of a pipe cleaner rather than a smooth line. The neutral can have a current flow that isn't anything you'd expect from resistive loads of same amperage.

It wouldn't surprise me if you experience flashing, beating or other malfunctions even if you connected two identical 120-277v fixtures in series across 240 or 277 with no neutral. The LED ballast front end has series filtration reactors and followed by capacitive load and you could end up with some wicked resonance that ends up blowing up the ballasts.

I am not understanding what problems might occur voltage wise here, tho I can see that a short across 480V would take out everything on that 3p breaker whereas a problem with 277V would do the same, just 1/3 as many lights. Yes, 277V requires a neutral. 480V doesnt.

For safety reasons and LED ballast frying prevention, all three breakers using the neutral should be handle tied or common trip though.

 

[dionysius]

well, I might see a problem with putting 20A worth of commercial/industrial (continuous load) lights on a 20A 277/480V breaker. 210.20(A).



You stuck with the 1/2" EMT as well? and see above for a potential code problem.

Unfortunately yes I am stuck with 1/2" for this.

As Smart stated the neutral is a current carrying conductor however it should be fine since #12 @90 C is rated 30 amps. 30 x .8= 24 amps

Since max OCPD for #12 is 20A and ampacity is 30A where is the code issue?? Derated for >3 CCC's it is 24A as pointed out above. In fact there is a 4A margin on the safe side. I wish I could use it.

So for a single set (to avoid a hard pull using 2 sets) is 8 per phase the max I can pack????

 

[ActionDave]

So for a single set (to avoid a hard pull using 2 sets) is 8 per phase the max I can pack????

Pulling eight 12s in half inch emt is very doable. A lot of guys on this forum whine about it, but it's not hard if you take your time and know how to hook your wires on the fish tape to make a small head. Use a little soap or some lemon pledge if you want.

 

[kwired]

Unfortunately yes I am stuck with 1/2" for this.



Since max OCPD for #12 is 20A and ampacity is 30A where is the code issue?? Derated for >3 CCC's it is 24A as pointed out above. In fact there is a 4A margin on the safe side. I wish I could use it.

So for a single set (to avoid a hard pull using 2 sets) is 8 per phase the max I can pack????

lighting is a continuous load, you can only load the 20 amp circuits to 16 amps, leaving you with six per line max.

7-9 CCC's derates to 21 amps.

 

[dionysius]

lighting is a continuous load, you can only load the 20 amp circuits to 16 amps, leaving you with six per line max.

I appreciate your input even if it is not exactly what I want to hear. I feel I will be dogged on this by Mr. Inspector so I want to be fore-armed. I see 16A as being over derated since I start at 30A and to get to 20A is 33.3% derated where only 20% is called for as I see it. I feel like I am leaving chips on the table. What am I not getting??? Is there any wiggle room???

 

[GoldDigger]

I appreciate your input even if it is not exactly what I want to hear. I feel I will be dogged on this by Mr. Inspector so I want to be fore-armed. I see 16A as being over derated since I start at 30A and to get to 20A is 33.3% derated where only 20% is called for as I see it. I feel like I am leaving chips on the table. What am I not getting??? Is there any wiggle room???

Your problem is that you specified a 20A non-100% breaker and that limits you to 16A under the code.
It does not matter how much oversized your wires are, they cannot make up for the small breaker they are attached to.


If you were able to use a 25A or 30A breaker the answers would be different.

 

[iwire]

Pulling eight 12s in half inch emt is very doable. A lot of guys on this forum whine about it, but it's not hard if you take your time and know how to hook your wires on the fish tape to make a small head. Use a little soap or some lemon pledge if you want.

:lol:

Work smarter not harder.

 

[ActionDave]

:lol:

Work smarter not harder.

I do. I'm a scrawny guy. It's the only way I can keep up.

 

[Smart $]

I appreciate your input even if it is not exactly what I want to hear. I feel I will be dogged on this by Mr. Inspector so I want to be fore-armed. I see 16A as being over derated since I start at 30A and to get to 20A is 33.3% derated where only 20% is called for as I see it. I feel like I am leaving chips on the table. What am I not getting??? Is there any wiggle room???

Pull two boats. Connect 36 fixtures. That's 150% of the 24 you started with. Take the victory and go home.

 

[JFletcher]

Pull two boats. Connect 36 fixtures. That's 150% of the 24 you started with. Take the victory and go home.

Yep. 8 CCC gives you 70% derating (310.15(B)(2) from 30A (#12, 90*C) giving 21A, still fine on a 20A breaker. the aforementioned code (or maybe 215.3) limits continuously loading a 20A breaker to 16A. I dont work with 277/480V breakers enough to know if you can get continuous (100%) ones or not... I suspect not, or if so, at 2x+ the cost.

Any lighting load of this type will be continuous (expected to be on 3hrs+).

If you cant do it with 2 boats ((3ph+neutral)x2), looks like you'll be installing another conduit or sending those 277V fixtures back for 480V ones.

Also be cautioned that fill tables from the 'net for 1/2" EMT vary a bit and arent always based on current code. Two I saw earlier, one was based on the 93 NEC, the other 99. More than 9CCC with #12 and you're gonna run into derating issues even if you can jam it in the pipe.

Pulling eight 12s in half inch emt is very doable. A lot of guys on this forum whine about it, but it's not hard if you take your time and know how to hook your wires on the fish tape to make a small head. Use a little soap or some lemon pledge if you want.

Slick the heck out of the run with WireGlide. It should look like Alien dripping snot from its face. When it comes to wire pulls, there is no such thing as "too much lube".

 

[dionysius]

Yep. 8 CCC gives you 70% derating (310.15(B)(2) from 30A (#12, 90*C) giving 21A, still fine on a 20A breaker. the aforementioned code (or maybe 215.3) limits continuously loading a 20A breaker to 16A. I dont work with 277/480V breakers enough to know if you can get continuous (100%) ones or not... I suspect not, or if so, at 2x+ the cost.

Any lighting load of this type will be continuous (expected to be on 3hrs+).

If you cant do it with 2 boats ((3ph+neutral)x2), looks like you'll be installing another conduit or sending those 277V fixtures back for 480V ones.

Also be cautioned that fill tables from the 'net for 1/2" EMT vary a bit and arent always based on current code. Two I saw earlier, one was based on the 93 NEC, the other 99. More than 9CCC with #12 and you're gonna run into derating issues even if you can jam it in the pipe.



Slick the heck out of the run with WireGlide. It should look like Alien dripping snot from its face. When it comes to wire pulls, there is no such thing as "too much lube".

You guys with your great experience and knowledge have me convinced. I truly appreciate the great help from this amazing website.

If I pull 2 boats do you strongly recommend 8 different colors???? Brown Orange Yellow White for boat 1......Red, Black, Blue Gray for boat 2 ???

I thought the breakers are all rated for continuous???? Perhaps not a given. Must I make this a specific requirement??? And pay more of course like you say......

 

[kwired]

You guys with your great experience and knowledge have me convinced. I truly appreciate the great help from this amazing website.

If I pull 2 boats do you strongly recommend 8 different colors???? Brown Orange Yellow White for boat 1......Red, Black, Blue Gray for boat 2 ???

I thought the breakers are all rated for continuous???? Perhaps not a given. Must I make this a specific requirement??? And pay more of course like you say......

Typical breakers used in a lighting panelboard are not rated 100%.

240.4(D) prevents you from putting more then 20 amp OCPD on a 12 AWG copper conductor, even though the 90C ampacity adjustment leaves you with a 21 amp conductor.

 

[ActionDave]

If I pull 2 boats do you strongly recommend 8 different colors???? Brown Orange Yellow White for boat 1......Red, Black, Blue Gray for boat 2 ???
.....

I strongly recommend you Don't. It is a needless complication and a code violation, 210.5. It's not hard to keep each set of hots and corresponding neutral grouped.

 

[kwired]

I strongly recommend you Don't. It is a needless complication and a code violation, 210.5. It's not hard to keep each set of hots and corresponding neutral grouped.

Whether or not it is a violation depends on if you have more then one voltage system at the premises, and if so what method you choose as identification. Color alone is a common ID method, but NEC doesn't restrict you to doing it that way.

 

[JFletcher]

You guys with your great experience and knowledge have me convinced. I truly appreciate the great help from this amazing website.

If I pull 2 boats do you strongly recommend 8 different colors???? Brown Orange Yellow White for boat 1......Red, Black, Blue Gray for boat 2 ???

I thought the breakers are all rated for continuous???? Perhaps not a given. Must I make this a specific requirement??? And pay more of course like you say......

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.

 

[Smart $]

...
If I pull 2 boats do you strongly recommend 8 different colors???? Brown Orange Yellow White for boat 1......Red, Black, Blue Gray for boat 2 ???

2 boats, both Brown, Orange, Yellow, and Gray, and 1 Green EGC. Tape one set—the whole set; not each conductor of the set—one color, and the second set another color. Re-label or tag if so desired after the pull.

I thought the breakers are all rated for continuous???? Perhaps not a given. Must I make this a specific requirement??? And pay more of course like you say......

The textbook requirement is that all breakers be capable of handling a load drawing rated current for a short time. Breakers must also be capable of carrying 80% of rated current indefinitely. That said, many breakers exceed these benchmarks. However, design and safety criteria are set according to these benchmarks rather than actual performance.

There's a lot more to using 100% breakers than just the breaker. For one, a 100%-rated listed panelboard and enclosure are required. Second, all the other breakers in that panelboard must be 100%-rated breakers. There are more caveats, but suffice it to say, it ends up being a lot of extra money for 20% extra capacity.

 

[dionysius]

2 boats, both Brown, Orange, Yellow, and Gray, and 1 Green EGC. Tape one set—the whole set; not each conductor of the set—one color, and the second set another color. Re-label or tag if so desired after the pull.


The textbook requirement is that all breakers be capable of handling a load drawing rated current for a short time. Breakers must also be capable of carrying 80% of rated current indefinitely. That said, many breakers exceed these benchmarks. However, design and safety criteria are set according to these benchmarks rather than actual performance.

There's a lot more to using 100% breakers than just the breaker. For one, a 100%-rated listed panelboard and enclosure are required. Second, all the other breakers in that panelboard must be 100%-rated breakers. There are more caveats, but suffice it to say, it ends up being a lot of extra money for 20% extra capacity.

Very well stated. I want to express my gratitude for this phenomenal help. I walked into this one kind of carelessly. It has made me become much more aware. In fact I am intent on having a serious talk with this customer during the week and opening him up to abandoning the existing 1/2" and moving to a 3/4" or 1" conduit.

You folks have inspired me and with the ammo I now have I am much more confident. If I go to 3/4" then would 10 AWG be more optimal???? Pigtailing the neutrals gets less inviting but is of course doable as the wire diameter increases is how I see it.

 

[JFletcher]

Very well stated. I want to express my gratitude for this phenomenal help. I walked into this one kind of carelessly. It has made me become much more aware. In fact I am intent on having a serious talk with this customer during the week and opening him up to abandoning the existing 1/2" and moving to a 3/4" or 1" conduit.

You folks have inspired me and with the ammo I now have I am much more confident. If I go to 3/4" then would 10 AWG be more optimal???? Pigtailing the neutrals gets less inviting but is of course doable as the wire diameter increases is how I see it.

How many lights total are going in? 2 boats gets you to 36 lights (6 per ph-->n x 6) on standard breakers. More than 36? Run another 1/2" pipe. Now you're at 72.

Still 1/2" EMT, 12ga stranded wire, 20A regular breakers.

Neutral will have to be pigtailied at every light anyway regardless of wire size. btw, the derating on 10ga at 70% (8CCC) is 28A, so you're not gonna get to use a 30A breaker; you'd be stuck with 25, if you can find them, and then 80% of that (20A). There is no advantage of using 10ga other than VD, which could be substantial at the last light (I'm assuming you dont have 20+ 650W lights packed into a tiny space)

btw, how do you plan on controlling/switching these lights?