Conductors of different systems 600 vs. 300 volts

[richwaskowitz]

I know about 300.3(C)1, but I am not sure if this applies to my question. We have some SEW Eurodrive motors coming in now with microswitches built in to the brake mechanism which monitor the status of the brakes. A cord from this switch enters the SEW motor's terminal box and two terminals are provided there, right next to the 480 volt motor power terminals for utilizing this switch in the control circuit. The question is, can this article (300.3) be cited to require that the field wiring entering this box to pick up the control circuit which will monitor this switch to have 600 volt rated insulation? Does a motor terminal box fall under "equipment wiring enclosure"? I am trying to argue that the control circuit wiring in the motor terminal box needs to be rated 600 volts also but the customer wants me to show them why.

 

[charlie b]

Does the equipment come this way from the manufacturer, and is it listed as a unit that was built in this way? If so, the NEC does not apply.

 

[richwaskowitz]

I am not referring to the manufacturer's wiring, I am talking about the cord I need to run into the same box to get pick up the switch from their terminals. They ran the switch into the box, i just need to go get it.

 

[augie47]

As 300.3(C)(1) tells you, all the wiring in the raceway, enclosure, etc must have an insulation no less than the maximum circuit voltage.
In addition, you need to make sure this circuit is not prohibited under Art 725.

 

[raider1]

Is this circuit a class 1, 2 or 3 circuit?

As Gus mentioned Article 725 regulates class 1, 2 and 3 remote control, signaling and power limited circuits and has specific requirements as to combining these systems with power and lighting circuits.

Chris

 

[richwaskowitz]

Class 1, remote control, non-power limited (I believe) since the switches in this circuit are suppliedby 110 vac control circuits protected by 10 amp breakers in an industrial control panel. The switches will be monitored by PLC inputs.

 

[raider1]

Take a look at 725.48 (2008 NEC) or 725.26 (2005 NEC).

Chris

 

[richwaskowitz]

Well, I just read more of 725 and it looks like 725.27(B) ends the discussion anyway as it requires all Class 1 conductors to have 600 volt insulation unless it is otherwise listed for Class 1 use. Agree or not?

 

[raider1]

Well, I just read more of 725 and it looks like 725.27(B) ends the discussion anyway as it requires all Class 1 conductors to have 600 volt insulation unless it is otherwise listed for Class 1 use. Agree or not?

Correct, Class 1 circuit conductors must have insulation rated at 600 volts.

Chris

 

[realolman]

I just had to replace the cord to a SEW eurodrive synchronous motor. The cord had three motor leads 2 - 24 vdc brake leads, and 2 thermal overload leads. In the same j box as those conductors , it had a 9 (used) conductor cord that terminated in a terminal strip for the resolver

Frankly , I didn't know what the heck to do... I posted a question about it on this forum and didn't get much response. Fortunately, I was able to google the markings on the cord, and get exactly the same stuff.

So what is the definitive answer? can you have 24 vdc (brake) and 5vdc (resolver ) and 400v (power) in the same cable, conduit, or j-box if the conductors are all 600v or not?

...and like I said in a recent thread, not allowing this stuff to be together seems to be a little outdated , and more than a little arbitrary With a thing like this motor, what else can you reasonably do?

 

[richwaskowitz]

Caution: Impending rant.

Realolman, I know I feel your pain. SEW motors are not from a different planet, but almost. Our customers are specifying these motors now with so much crap being funneled into the terminal box that we don't know what to do either. In a typical 5 hp brake motor, inside the motor terminal blox there is the terminal block for the 6 motor leads, a rectifier with 5 terminals where the 460 volt AC brake power is turned in to who-knows-what DC to the brake coil, and now four terminals where these two micro switches come in from the brake mechanism to indicate when the brake is released and when it is wearing. We have to bring in two separate power cables; one shielded 3 conductor for 460 v motor power from the VFD, one shielded 2 conductor for 460 v brake power, and now a cord with a 120 v control hot and take back two PLC inputs. PLUS, there is a brake control relay module which takes up one of the 1/2-14 npt conduit opening also. That means there needs to be SIX threaded conduit openings in this little 4x5 inch cast iron box.

We also do not know what to do (practically) to accommodate all this stuff. In my opinion, those micro switches should have never been taken into that box by SEW.