277V Baseboard heaters off of 3PH/480V power supply 1

[Dracula7]

Hi
I have to install 12ea 277V/2.5KW baseboard heaters into a tunnel (that's how we call it)that is feed by 480/3Ph line.
6ea will have to go on left wall and the other 6 on the right wall.
I plan to use 1st and 4th heater from phase A, 2nd and 5th from B, and 3rd with 6th from C phase for left wall and same for right wall. My question is how I size the cable that will feed each side of the wall(it's a 25' type SOOW or type W - not sure yet what to use)? Second question - what will be the size for the breaker?
If I'm right, each side of the wall will have 5kw of load/phase (2.5 KW x 2 heaters)and by 277 V (line to neutral) will be 18 A/phase. If we add the continuous load (x25%) that total to 22.5 Amps per phase per side. If the cable it's a type SOOW then what size the wire should be?
Also, in this case is the neutral considered a carrying conductor?
22.5A x 2(sides) = 45 A which means a 3ph/50 Amp breaker - Is this correct?
I hope I was not too confused in explanation but some local electrician believe that I'm wrong and I will like to know where.
Thank you in advance for any explanation!

 

[LionelHutz]

If you're going to use a 50A breaker then the cabling all needs to be suitable for 50A as well which likely means you need to use 6 gauge wire.

You are correct that the heaters on each wall would draw 18.5A 3-phase and yes you would need a cable with 3-phase and 1-neutral conductor. I'd think a 10 gauge cable would work for that by using 30A protection on the cable.

 

[resqcapt19]

If this is an NEC application, you probably can't use SOOW or type W cables. See 400.7 and 400.8.

 

[Dracula7]

Thanks both for your input.
I did plan for using the 5C/10GA cable for each side but I just want it to make sure I'm right. Thanks for the reference to the NEC code, but I forgot to mention that this equipment is a movable part and this is the reason I'll have to use a cord.

 

[melspuds]

Wo! Slow down. I see some possible real problems here with this project. We need more info from you before you start on this project.
1) Is this for tunneling or mining in any way? If it is MSHA applies.
2) How are you controlling the heaters? One thermostat, one stat per side, or 12 thermostats. This is important for the wire sizing of the neutral.
3) What are the heaters being used for? Is it an environment that is hazardous or combustible.
4) Are the heaters UL approved for the use that you are intending for. I do not know of any baseboard heaters that are approved movable equipment. Baseboard heaters to my knowledge, are only to be mounted on vertical rigid member and not to be moved around. The heating element just hangs 3 or 4 little hangers. I could be wrong, but a baseboard type heater for your use, is an accident waiting to happen. What you need is industrial type strip or infrared heaters.
5) What is the stated wire temperature in the heater junction box.
Good luck and will be waiting for the info from you.
Dave

 

[Dracula7]

Dave, thanks for your response,
1. No it's not mining
2. The heaters will be controlled by a single thermostat that will latch/unlatch a 3 phase contactor
3. None of the hazardous or combustible
4.They are UL listed, but the tunnel will have slow motion and relatively for really short distances. They will be installed in Passenger Boarding Bridges for Airports to warm them up while the passengers walk through. Anyway, the heaters will be installed on fix walls, on 2" legs
5.Not sure

 

[melspuds]

I take it that the thermostat will be on a tunnel wall.
I need more info from you.
1) Were is the contactor located, is it going to be also on a tunnel wall?
2) Can conduit be run from one wall to the other wall via the ceiling?
3) Need info UL listing or nameplate info of a heater, such as wire temperature in j.box,voltage, overcurrent protection, wattage, can the units be connected on either end, and is there a wiring trough for extra wires.
4) What type of material is the wall going to be, that the heaters are mounted to?
5) What is the voltage rating for the thermostat and contactor coil?
Good hunting,
Dave

 

[jraef]

Are you sure that you have 480Y277V power? A lot of industrial facilities still have 480V delta power, which will NOT work for you. If you don't know, look at your incoming service. You would have 3 power lines, a white marked neutral, and a ground conductor, which may or may not be bonded at your service entrance. Measuring the lines and reading 277V line to ground is no guarantee that your service has a neutral. You can get a floating voltage reading of 277 to ground, but it's not the same.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[davidbeach]

Also, aren't there height limitations in the code that would keep you from installing that equipment at that height? It's been several years since I have looked, so things may be different than I remember.

 

[melspuds]

davebeach & jraef,
This supposedly is a temporary "airport passenger boarding bridge". All of the airport terminals that I have worked with use 480/277v for most equipment (HVAC, lighting, ramp equip, ect), including baseboard heating. What I am concerned about is the mounting wall material, overcurrent protection per unit, need of gfi, and wiring temperature ratings.
Dave

 

[Dracula7]

Dave,
you are correct - thermostat will be on the tunnel wall
1. - Contactor will be located about 12' away from tunnel into a Disconnect Panel - this is the reason for the Type W cable connection
2. - No
3. - I don't have the plate (and not for another month, since the equipment is on site already and won't get to install it for a month) but the what I know is: 277V, 2500W, OCP - I think is 20Amp, with 9 Amp/unit. yes they can be end connected and have wire trough at bottom rear all alongside.
4. - Walls are made out of some special wallboard, fire rated,... industry specific - but not sure exactly what kind.
5. - Thermostat/contactor will be on separate circuit 110V at 25Amp rating for thermostat and contactor is a 90Amp with 110V coil rating
David - the 2' legs are not an issue in this case
Jraef - we are good on the voltage. It did happened not long ago to have Delta incoming and the VFD's were not working properly (big headache for me at that time until I figure it out)
Thanks again to all for involving in this tread.

 

[waross]

Hire someone who knows what he is doing.
A free forum on the internet is not the place to plan 480/277 Volt installations that will be accessed by the public.
Flexible cable is generally only acceptable for the portion of the run that needs to be flexible.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[melspuds]

Dracula7
1) Is there a roof on this "tunnel"?
2) Are the heaters listed for wet locations?
3) Are you sure about the listed overcurrent protection is 20 Amps? If so, then you need 2 circuits per side. You will need a 60 Amp 3 pole 480/277V feeder breaker, contactor, 4-20 Amp 3 pole 480/277V Branch circuit breakers, and 4-20 Amp 5 pole 480/277V receptacles and attachment plugs per site specs, 4 lengths of 12AWG 5C cords, 4 cord grips, 4 sized junction boxes/covers, 12AWG 90C^o Cu wire with colors per sites color coding, 1/2" conduit and fittings, ect.
4) Is it 2 inch or 2 foot legs? If 2 ft you will have trouble passing inspection with AHJ.
5) Are you sure about the voltage at the site is 480/277 Volts, which is Wye system not a delta system?
6) Where is the thermostat getting 120 volts from? Should be from the 60 Amp feeder breaker thru a 277/120V control transformer with primary and secondary fusing. The reason behind this is one disconnect shuts off all power to the system. You are going to need also 1 length of 14AWG 3C cord, 1- 15 Amp 120V twist-lock receptacle and attachment plug per site specs, cord grip, junction box/cover, 1/2" conduit and fittings, 14AWG 90^o Cu wire per site color code.
Good luck,
Dave

 

[melspuds]

Dracula7
What is the Short-Circuit Current Rating ( SCCR ) at the point of connection to your 60Amp breaker going to be. Also you might need mechanical interlocks on your receptacles.
I agree with waross you should hire a licensed electrician and have them pull a permit for the job.
Dave

 

[Dracula7]

Thank you all for your help