Jraef
How do you read section 432 (A) (1)?
I read it as a thermal overload device such as a 3 thermal heater relay units .
BJ,
I can appreciate your position on this and I don't totally disagree with your premise, it's just that I think you are discussing the technical issues, I was discussing the CODE issues.
Assuming you meant 430.32 (A) (1) because there is no 432...
As I was taught and have interpreted it, 32 establishes that there SHALL BE overloads, 37 was added to tell us how many.
If the vendor of the combination starter has drawings showing two of the heaters being used to sense motor overload that meets the requirement.
As with many issues like this, if an equipment manufacturer has a piece of equipment NRTL listed in this way, then as the installer, your job is done. You don't need to 2nd guess them. But they PAID BIG BUCKS to have that done* and if they did it with 2 OLs to save $2.32 per controller, it's because they sell a LOT of controllers. For us in the field however, we cannot do this on our own without violating 430.37. By the way, I don't know of any manufacturer of standard electro-mechanical 3 phase starters that is still using 2 OL protection, it just isn't worth it for them.
Does 430.37 refer to sensors or protection devices?
Some manufacturers of HVAC equipment use two pole contactors to control three phase motor on there equipment. I don't like it but there is a section of the code that allows it. I was reading section 430.37 as making sure people didn't use a 2 pole relay to stop a 3 phase motor.
430.37 specifically says "...overload units such as trip coils or relays". This is not the part that references contactors etc., that is a separate issue. This entire section is about motor
protection. Don't get me started about HVAC manufacturers, but let's just say "minimally acceptable" is the primary design criteria for them. What they are doing is banking on 430.38, which describes HOW an OL device will stop a motor.
"...shall simultaneously open a sufficient number of ungrounded conductors to interrupt current flow to the motor" is a statement of minimally adequate design, and they jump all over it.
Two motor overload sensors can adequately protect a motor from overheaing. I have use two overload heaters to stop a motor and the third as an alarm. The heater size on the alarm unit is one or two sizes less than the other two. It pass the 05 code. I don't think the inspector would have caught it but we brought it up and explained the purpose.
Monitoring 2 phases of a motor can adequitely protect a motor from Overload ( not the motor or conductors from short circuit).
Overload on a TOCC plot shows up way to the left of the fuse, or circuit breaker or cable damage curves.
The solid state units have an alarm built in so I don't expect to have to do it anymore.
I never said it would not work, but it is specifically forbidden in the NFPA 70 Code, section 430.37 and they had their reasons when they did it in the late 70s. Every inspector is the Authority Having Jurisdiction however; "the Demigod of his own little world"; and if he decides you have made a valid argument, then he can accept it, even if another inspector would not. It is still technically a code violation so just because one inspector accepted it, that doesn't mean anyone can do it and get another inspector to think the same way. Many have tried... and failed, in things like this as many members of this forum will attest to.
* I have an example but it's a tangent so I'll put it in a separate post to avoid this one being so much longer.