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 AndrewF 02-08-2011 10:50 PM

Cable Wheel - # Circuits

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A local church recently purchased a spring cable management wheel for getting electric to a truss that can be raised and lowered over the stage.

I became involved in the project after the fact and am trying to figure out if the company that sold them the wheel, sold the right one. I handle the lighting as a volunteer for weekend services and am trying to figure out the maximum number of lighting circuits the truss is capable of having.

http://www.conductix.us/products/cab...powerreelc2ae/

The whip for the wheel has 12 - 12 gauge stranded wires on it.

My question pertains to how many usable circuits that can provide based on the following:

There are two winches on the truss that raise and lower anything hung from the truss, usually a projection screen. These require 3 wires each, plus ground.

I wanted to have a single 208-240 service on the truss along with as many 110 circuits as possible.

Where I am confused is knowing the size of the wire is fixed at 12 gauge, how does a MWBC work in this setup?

Can we do

208/220 circuit #1
1 - 110 phase 1
1 - 110 phase 2
1 - 110 neutral (shared with cir #2)

208/220 circuit #2
1 - 110 phase 1
1 - 110 phase 2
1 - neutral (shared with cir #1)

So that uses 5 wires.

Then for the winch motors which require independent control.

Motor #1
1 - up
1 - down
1 - neutral (shared with motor #2 neutral)
(The positive comes from the wired remote switch)

Motor #2
1 - up
1 - down
1 - neutral (shared with motor #1 neutral)

That uses another 5 wires, leaving me with 2 left.

Can the electrician make these one 110 circuit, sharing the neutral of the motor circuits and a ground?

The issue (IMHO) is the company that sold the wheel, didnt listen to the requirements and wasnt responsible for the installation of the wheel.

Note: The installation will be done by a local electrician. What I am trying to figure out is if this wheel will do what we need it to do, before I haul the thing up in the ceiling...its about 60' up there thru a small hatch.

 AllanJ 02-09-2011 08:17 AM

One neutral may serve no more than two hot wires on opposite sides of a 120/240 volt single phase circuit, or no more than three hot wires each on a different phase of a 120/208 volt 3 phase crcuit.

So your five wire clusters cannot be done.

You would use 3 wires each for Circuit 1 and Circuit 2. These are MWBC's.

One MWBC can have both 120 volt and 240/208 volt receptacles and loads.

The two motors must be on the same 20 amp circuit to share a neutral (can also be a MWBC with one motor on each side of the line).

You have one wire left. It is needed as a ground wire.

Oops, let me give one alternative: If the total load, motors and all, is 40 amps or less divided into two 20 amp allotments you can have four or five hot wires with individual switch control down below and one neutral for everything, all served by one 20 amp MWBC going down to the breaker panel.

Check the wattage ratings for the reel. It is possible that the cord in the reel cannot take 20 amps on all those circuits simultaneously due to heating (the process of determining how little it can take compared with 12-gauge-equals-20-amps is called derating). So it is possible that you don't need and can't use more than one 20 amp MWBC coming up from the panel, or maybe two including the requirements for the motors.

Another thing you could look into is wireless remote control switches and dimmers up on the truss, so only a small number of unswitched power circuits carrying the full 20 amps each need use the wires in the reel.

 AndrewF 02-09-2011 09:09 AM

Quote:
 Originally Posted by AllanJ (Post 587547) Check the wattage ratings for the reel. It is possible that the cord in the reel cannot take 20 amps on all those circuits simultaneously due to heating (the process of determining how little it can take compared with 12-gauge-equals-20-amps is called derating). So it is possible that you don't need and can't use more than one 20 amp MWBC coming up from the panel, or maybe two including the requirements for the motors. Another thing you could look into is wireless remote control switches and dimmers up on the truss, so only a small number of unswitched power circuits carrying the full 20 amps each need use the wires in the reel.
Good point, I'll have to grab the book that came with it and see what it is derated to.

All the fixtures on the truss are intelligent fixtures controlled via DMX. The circuits that power these fixtures are always on.

I am guessing a second wheel will have to be purchased to get the correct number of circuits up there, as the eletric hoists consume too many.

Right now, anytime the truss is lowered and raised, someone has to go up in the ceiling and unspool the current cables which is a hassle.

 brric 02-09-2011 09:12 AM

Quote:
 Originally Posted by AllanJ (Post 587547) One neutral may serve no more than two hot wires on opposite sides of a 120/240 volt single phase circuit, or no more than three hot wires each on a different phase of a 120/208 volt 3 phase crcuit. So your five wire clusters cannot be done. You would use 3 wires each for Circuit 1 and Circuit 2. These are MWBC's. One MWBC can have both 120 volt and 240/208 volt receptacles and loads. The two motors must be on the same 20 amp circuit to share a neutral (can also be a MWBC with one motor on each side of the line). You have one wire left. It is needed as a ground wire. Oops, let me give one alternative: If the total load, motors and all, is 40 amps or less divided into two 20 amp allotments you can have four or five hot wires with individual switch control down below and one neutral for everything, all served by one 20 amp MWBC going down to the breaker panel. Check the wattage ratings for the reel. It is possible that the cord in the reel cannot take 20 amps on all those circuits simultaneously due to heating (the process of determining how little it can take compared with 12-gauge-equals-20-amps is called derating). So it is possible that you don't need and can't use more than one 20 amp MWBC coming up from the panel, or maybe two including the requirements for the motors. Another thing you could look into is wireless remote control switches and dimmers up on the truss, so only a small number of unswitched power circuits carrying the full 20 amps each need use the wires in the reel.
MWBCS are only allowed to serve line-to-neutral loads.

 AndrewF 02-09-2011 11:25 AM

 frenchelectrican 02-10-2011 01:25 AM

There is other issue some of you may overlook on this one if the reel is pretty much retracted { wind up with cord or cable } when you run the power on this near full load it will get hot { try that with roll of 50" with 12-WG romex but do not uncoil it and run a heater or simauir load you will see why }

Merci.
Marc

 AllanJ 02-10-2011 07:54 AM

The instructions may say that the cable must be completely unwound from the wheel prior to use even if the truss is lowered only a small amount.

Many vacuum cleaners and similar appliances with retracting cords require that the cord be pulled out all the way prior to use.

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