Cable protection for Class 30 overload application with soft starter - MCP or thermal magnetic MCCB 1

[123MB]

Hi Guys,

I am in Australia where we use IEC standards and we don't have any requirements for UL listing of protective devices.

We have a class 30 overload application with a soft starter with line contractor. What sort of branch protection should I be using?

The distributor is telling me that we should use a magnetic only (you guys call it an MCP) breaker upstream and let the soft starter do overload protection for the feeder cable, motor cable, and contactor.

What do you think? Will the thermal protection in the soft starter protect the feeder cable and motor cable, even if the soft starter is set up for a class 30 overload?

What about the contactor? can the soft starter be relied upon to do thermal overload protection for it too?

Cheers

 

[VicP]

True, but as I said, no longer for VFDs and Soft Starters, as of I think 2014, maybe early 2015. They stopped allowing NEW submissions like that even longer ago, around 205 or 6 IIRC, but were not forcing "grandfathered" designs to be changed change. That's what ended recently; even older grandfathered designs are no longer acceptable with MCPs, the breakers must be T-M.

jraef
I would be interested in seeing the specification which prohibits using a MCP with a VFD. I am particularly interested in the CSA specification. Can you provide me with any references?

Thanks

 

[jraef]

Well there is no specification that explicitly prohibits it as far as I know, but mag-only breakers have always been only "Recognized Components", not "Listed" by UL. That means they cannot be used stand-alone, they can ONLY be used in listed combinations as part of a complete assembly. So what changed is that UL stopped accepting complete assembly tests on VFDs and Soft Starters that include nag-only breakers. This actually took place a while ago but they allowed assemblies that were already listed with MCPs to continue to be listed, until last year (or 2014). I think it had been a 10 year "grace period" IIRC.

I can't speak to CSA, but in general they tend to follow each other's rules.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[waross]

jraef
I would be interested in seeing the specification which prohibits using a MCP with a VFD. I am particularly interested in the CSA specification. Can you provide me with any references?

Thanks

Is this what you are looking for?

28-210 Instantaneous-trip circuit breakers (see Appendix B)
When used for branch circuit protection, instantaneous-trip circuit breakers shall be
(a) part of a combination motor starter or controller that also provides overload protection;
and either
(b) rated or adjusted, for an ac motor, to trip at not more than 1300% of the motor full load current or at not
more than 215% of the motor locked rotor current, where given, except that ratings or settings for trip
currents need not be less than 15 A;
or
(c) rated or adjusted, for a dc motor rated at 50 hp or less, to trip at not more than 250% of the motor full
load current, or for a dc motor rated at more than 50 hp, to trip at not more than 200% of the motor full
load current.

We can only use MCPs as part of an approved assembly. We cannot use MCPs for field built controls.
If we can find a VFD that is part of an approved assembly with an MCP, we may use it. We cannot use an MCP for either a magnetic motor starter or a VFD for field built assemblies.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

That says you could use it with any starter which has an overload. Where does it say you can only use it as part of an approved assembly?

 

[waross]

Lionel, the key words are "Combination Starter", not "any starter".

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

The NEC wording is essentially the same, although it adds the term "factory assembled and listed combination". I can't recall the exact paragraph and I'm on my phone, but I think it's embedded in 430.52 somewhere.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[LionelHutz]

Yes, CSA doesn't say it has to be a listed combination, just a combination.

 

[iceworm]

jraef essentially got it:

(3) Instantaneous Trip Circuit Breaker. An instantaneous trip circuit breaker shall be used only if adjustable and if part of a listed combination motor controller having coordinated motor overload and short-circuit and ground- fault protection
in each conductor, and the setting is adjusted to no more than the value specified in Table 430.52.

Informational Note No. 1: Instantaneous trip circuit breakers are also known as motor-circuit protectors (MCPs).

NEC 1996 reads essentially the same.

However, no factory assembly requirement. Still one would have to get the assembly field listed - that definitely could be a problem if the NRTLs don't like it - and plenty of money.

I'm a bit surprised NRTL agencies won't list ASDs with a mag-only CB. Their usual concern is only that the device not start a fire - not that it actually works. Self-destruction is only an issue if it causes a fire.

Interestingly, 2014 NEC 430.130.A specifically allows instantaneous CBs with ASDs. Still have to be listed.

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[LionelHutz]

Yes, a small but important difference between CEC and NEC. The word "listed". But NEC also requires ground fault protection.

And going back to the previous comment from waross,

breaker + starter having an overload (ie a contactor and overload) = combination motor starter

 

[waross]

"breaker + starter having an overload (ie a contactor and overload) = combination motor starter" PLUS installed in an enclosure with an operating handle that is interlocked with the door latch. Not a field built assembly.
Listing or approval is covered in section 2

2-024 Use of approved equipment (see Appendices A and B)
(1) Electrical equipment used in electrical installations within the jurisdiction of the inspection department shall
be approved and shall be of a kind or type and rating approved for the specific purpose for which it is to
be employed.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

I've run into many cases of people building their own starter from listed components. We sell people the parts to do it all the time. Around here, the ESA will approve a field built combination motor starter.

 

[waross]

With all respect for your expertise and experience, Lionel;
We have all seen instances of an installation that was passed by one AHJ and failed by another. Most of us have seen installations passed by an AHJ that maybe should not have been passed.
I fondly remember one local inspector and a number of imported ticketing machines that required local approvals. All our inspector looked at was the serial number. If the number was correct, the machine passed.
Then one day the customer changed out a faulty machine without letting me know. The number was wrong. The inspector just drew a line through the number on the paper work and wrote in the correct number and passed the machine.
Passing inspection in one jurisdiction does not guarantee that an installation is universally approved.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

Posting about how an AHJ passes when they shouldn't has no relevance here. IT'S ALLOWED BY THE CODE. The AHJ using the CEC is simply WRONG if they refuse to accept it.

 

[Marke]

On the EMX3, parameter 1B is the maximum Locked Rotor time and this determines the overload curves of the protection.
Default is 10 seconds which is the equivalent of a class 10 overload.
For high inertia loads, you need to first have a motor capable of a long locked rotor current, (mining duty motors are commonly 40 seconds) and set parameter 1B accordingly.

Best regards,
Mark.

Mark Empson
Advanced Motor Control Ltd