I'm designing a bull rail with 22 GFCI outlets on individual circuits fed from a power pack XFMR. This means I will have 22 hots, 8 neutrals and 1 ground. According to NEC table 310.15(B)(2)(a) I must de-rate the ampacity of my current carrying wires by 45%. This forces me to use #8AWG wire and, therefore, 2" conduit. I would think on a bull rail this wouldn't apply or there is something in the code that addresses this. All I have heard from electricians is that they just break the code and use #12AWG wires. Does anyone have any idea on this one?
Bull Rail de-rating
- Thread starter cainta
- Start date
- Status
- Location
- Massachusetts
Re: Bull Rail de-rating
Seriously, consider running three or four 3/4" raceways spread out over the length of the 'bull rail' whatever the heck that is.
Yes, do not run them all in one pipe.
Seriously, consider running three or four 3/4" raceways spread out over the length of the 'bull rail' whatever the heck that is.
Re: Bull Rail de-rating
(Maybe 'bull rail' is just an Alaskan term, it is used in parking lots to plug vehicle engine blocks in to keep the oil warm in sub-freezing temperatures.)That is how I decided to design it to comply with NEC by using (2) 1-1/2" conduits and everyone that saw this design thought I was crazy.
(Maybe 'bull rail' is just an Alaskan term, it is used in parking lots to plug vehicle engine blocks in to keep the oil warm in sub-freezing temperatures.)That is how I decided to design it to comply with NEC by using (2) 1-1/2" conduits and everyone that saw this design thought I was crazy.
ryan_618
Senior Member
- Location
- Salt Lake City, Utah
Re: Bull Rail de-rating
That still doesn't comply. You are talking about a 20 amp circuit, right?
That still doesn't comply. You are talking about a 20 amp circuit, right?
- Location
- Massachusetts
Re: Bull Rail de-rating
That makes sense.
If you use 10 AWG and three raceways you will be in good shape.
Hey you might be able to take advantage of the temperature correction factor below 310.16 that lets you up rate the wire by 1.05.
Why, does it get cold there?
That makes sense.
The 'magic' number is usually no more than 9 current carrying conductors per raceway before you have to up size the wire.
If you use 10 AWG and three raceways you will be in good shape.
Hey you might be able to take advantage of the temperature correction factor below 310.16 that lets you up rate the wire by 1.05.
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: Bull Rail de-rating
You really don't want to open that can of worms, do you?
- Location
- Massachusetts
Re: Bull Rail de-rating
Originally posted by charlie b:
You really don't want to open that can of worms, do you?
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: Bull Rail de-rating
For those who wonder about my "can of worms" reference, consider this: If the temperature in Alaska is below 60 for most of the year, but it goes above 78 for a couple of hourse on one or two days a year, do you lose your ability to apply the 1.05 "up-rating" factor?
For those who wonder about my "can of worms" reference, consider this: If the temperature in Alaska is below 60 for most of the year, but it goes above 78 for a couple of hourse on one or two days a year, do you lose your ability to apply the 1.05 "up-rating" factor?
sheldon_ace
Member
- Location
- Owego, NY
Re: Bull Rail de-rating
By the rules "yes", by using common sense "no". Thats like calling a receptacle that someone might plug a temporary appliance that draws 16.5 amps for three and a half hours and consider it a "continuous load".
websparky
Senior Member
- Location
- Cleveland, Ohio
Re: Bull Rail de-rating
Just because the receptacle is rated at 20A doesn't mean the load is 20A. What would be wrong with 12AWG if the load was 13A? What if you used 10AWG and the load was 20A?
Just because the receptacle is rated at 20A doesn't mean the load is 20A. What would be wrong with 12AWG if the load was 13A? What if you used 10AWG and the load was 20A?
- Location
- Illinois
- Occupation
- retired electrician
Re: Bull Rail de-rating
Dave,
Don
Dave,
Yes, but if you have to derate below 20A for the #12, then you can't use a 20A OCPD.
Don
websparky
Senior Member
- Location
- Cleveland, Ohio
Re: Bull Rail de-rating
Don,
You are correct, as usual. However, there was no mention of the size of the overcurrent protection.
Don,
You are correct, as usual. However, there was no mention of the size of the overcurrent protection.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Re: Bull Rail de-rating
Okay, next question: What is the current consumption of a typical blcok heater? There may not need to be that many (22) circuits.
Okay, next question: What is the current consumption of a typical blcok heater? There may not need to be that many (22) circuits.
Re: Bull Rail de-rating
Posted by Charlie B:
Posted by LarryFine:
Steve
[ October 06, 2005, 09:15 AM: Message edited by: steve66 ]
Posted by Charlie B:
If it is 78 out, nobody will need the block heaters, and even if they plugged them in, I would think thermostats would keep them from actually drawing a load.
Posted by LarryFine:
I think block heaters do draw a pretty large load. Just taking a guess, it might be 1500W. But I am just guessing. I am sure someone will correct me if I'm wrong.
Steve
[ October 06, 2005, 09:15 AM: Message edited by: steve66 ]
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: Bull Rail de-rating
My use of the "78 degrees for a couple hours" was intended to be generic, not related to these block heaters. I was trying to discourage taking credit for having ambient temperatures below 30C to up-rate the ampacities. I think the rule is not at all clear.
My use of the "78 degrees for a couple hours" was intended to be generic, not related to these block heaters. I was trying to discourage taking credit for having ambient temperatures below 30C to up-rate the ampacities. I think the rule is not at all clear.
Re: Bull Rail de-rating
The 'power pack' that feeds the 22 GFCI outlets has 20A breakers. We need all 22 outlets because there is a potential of 22 vehicles that need block heaters. In the winter in Alaska if you leave a vehicle outdoors unplugged it probably won't start. The block heaters for the equipment we will be using on average is about 500W. Plus a 'bull rail' has a tapering effect where you would lose 4 circuits in the conduit every 10'.So, I think that it would be safe to use #12 in one 1-1/4" RMC. But, by code to use #12 I must have 4 runs of 3/4" RMC. If I want to use one conduit run by code I must use #8 and 2" conduit, #8 of course won't land on any terminals so an abundance of splicing must be implemented. Does this piss anyone else off? I think it is ridiculous.
The 'power pack' that feeds the 22 GFCI outlets has 20A breakers. We need all 22 outlets because there is a potential of 22 vehicles that need block heaters. In the winter in Alaska if you leave a vehicle outdoors unplugged it probably won't start. The block heaters for the equipment we will be using on average is about 500W. Plus a 'bull rail' has a tapering effect where you would lose 4 circuits in the conduit every 10'.So, I think that it would be safe to use #12 in one 1-1/4" RMC. But, by code to use #12 I must have 4 runs of 3/4" RMC. If I want to use one conduit run by code I must use #8 and 2" conduit, #8 of course won't land on any terminals so an abundance of splicing must be implemented. Does this piss anyone else off? I think it is ridiculous.
Re: Bull Rail de-rating
You are running 31 conductors to the first receptacle, and dropping conductors as you go down the row?
How big a box are these receptacles mounted in (at least at the beginning of the run)
Seems 3 or more runs would make life a lot easier?
You are running 31 conductors to the first receptacle, and dropping conductors as you go down the row?
How big a box are these receptacles mounted in (at least at the beginning of the run)
Seems 3 or more runs would make life a lot easier?
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