UL 508 & NEC

[semore_sparks]

I see the leading vendors of MSP's (motor starter protectors) using statements mentioning UL 508 type(E)(F) rating and no need for upstream "short circuit protection" for these devices. The Fuse guys
say "As long as it doesn't blow the door off", these devices can pass UL 508. Sometimes you may see small
print saying "May need separate short circuit protection". What happened to motor/branch circuits and UL 489 breakers or fuses as a requirement for compliance with NEC? Can a panel with MSP's used as UL 489 CB's pass NEC?

 

[templdl]

Re: UL 508 & NEC

The "May need separate short circuit protection" doesn't make sense. There's a couple of things to consider when using devices in series. Either they are series rated as you would apply fuses and breakers, or combination rated as would be a combination motor starter. In either case the devices must be tested and listed by UL for the applicaiton to get a given rating. You can't magically apply a a short circuit protective device and expect it to protect and limit or prevent damage to down stream devices.
Yes, the statement of "As long as it doesn't blow the door off" is true even with breakers.
The object is to keep all of the parts and pieces inside the cabinet.

 

[ron]

Re: UL 508 & NEC

I'm not sure I understand the question, but ....
A motor circuit protector is a magnetic only version of a regular thermal magnetic circuit breaker (thermal element not included). A MCP in conjunction with a "heater" (overload) to perform the thermal part of the protection you only need upstream protection for the cable.

 

[jim dungar]

Re: UL 508 & NEC

Ron, in this case the phrase "Motor Starter Protector" is a device that contains adjustable motor overload protection as well as short circuit protection. Many people call these IEC style manual starters (Look at SQD type GV2 and A-B 140M).

From Square D's catalog: "...devices are UL Listed for group installations for motors with individual full-load currents up to 63A. If each motor in a grouping is controlled by a GV2 or GV3 device, only one branch circuit protective device...is necessary for the entire group. ... in accordance with National Electrical Code Article 430-53."

A UL 508 Type E self protected starter is applied the same as any other combination starter (i.e. single motors).