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Power limited cables. What does that mean? #206921
09/01/12 06:51 PM
09/01/12 06:51 PM
L
LarryC  Offline OP
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
I document cable assemblies for use in machines. Ocasionally I see people selecting a "power limited cable" to supply AC or DC power to subassemblies. I am confused as to what a pwr limited cable is.

Can someone explain?

Thanks.

Work Gear for Electricians and the Trades
Re: Power limited cables. What does that mean? [Re: LarryC] #206922
09/01/12 08:19 PM
09/01/12 08:19 PM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,166
Estero,Fl,usa
It is a circuit where the power is limited by the source, like a wall wart or other small power supply. This is defined better in Table 11 in the back of the NEC.
This usually refers to 725 class 2 & 3 circuits.

In 725 Class 1 circuits this may not be all that "limited" but you will also be using wiring methods that look like chapter 3.


Greg Fretwell
Re: Power limited cables. What does that mean? [Re: gfretwell] #206927
09/02/12 10:50 AM
09/02/12 10:50 AM
L
LarryC  Offline OP
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
That makes sense when talking about power limited circuits.

What I am asking about is when power limited is part of the cable description. For example: 3043A Multi-Conductor - 300V Power-Limited Tray Cable. This is a 2 pair 16 AWG shielded cable from Belden.

I want to use this cable to supply two AC circuits to a remote location in the machine. How does the power limited part of the description affect my choice in using this cable?

Thanks.

Re: Power limited cables. What does that mean? [Re: LarryC] #206928
09/02/12 11:33 AM
09/02/12 11:33 AM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,166
Estero,Fl,usa
Inside a machine, you are really outside of the NEC world. This might affect the listing of the machine but I have never actually seen that be brought up and we altered our machines all the time. As long as you are within the voltage rating and ampacity of the cable, with the proper O/C protection, you should be fine. I would also be looking at the exposure to damage. The biggest problem we saw with cables was flexing, chafing, pinching and other casualties.


Greg Fretwell
Re: Power limited cables. What does that mean? [Re: gfretwell] #206929
09/02/12 11:40 AM
09/02/12 11:40 AM
L
LarryC  Offline OP
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
That is my thought too. I am just trying to understand the differences between a power limited cable and non power limited cables. I am wondering if there are differences in contruction, materials used, or test methods for determining ratings.

I understand that mil spec type E wire is rated for 1000V but the same construction is only listed for 300V by UL specs.

I wonder if the power limited specification changes the test method or rating method used to determine the cable ratings.

Re: Power limited cables. What does that mean? [Re: LarryC] #206931
09/02/12 11:59 AM
09/02/12 11:59 AM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,166
Estero,Fl,usa
I think it is just where these cables appear in the NEC. Beyond that, you have 725 cables that are more capable than non metallic cables in chapter 3.
There is nothing in a NM cable in chapter 3 that is plenum rated.


Greg Fretwell

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