SCCR, or not SCCR for solid-state relays

[MFS-PDX-313]

I'm going to use a solid-state relay for controlling a 208V single-phase heater by turning it on/off. Basically, it's a transistor contactor. The power will come off of a main three-pole breaker, to a bus, then from the bus to a two-pole breaker, one leg of the breaker will go through the SSR to the heater and the other leg will go directly to the heater (see attached)



When I had done a three phase heater design in the past, the three phase SSR had a SCCR value listed in its spec sheet. The SSR that my manager want to go with for this project, an RSCDN-30A from IDEC, didn't list an SCCR value. When I contacted IDEC, they informed me that it did not need an SCCR value because it's part of the control circuit, not the power circuit. Am I wrong thinking that this 30A SSR should be part of the power circuit?

 

[hbiss]

When I contacted IDEC, they informed me that it did not need an SCCR value because it's part of the control circuit, not the power circuit.

That doesn't make sense.

-Hal

 

[petersonra]

It is clearly part of the power circuit.

The spec sheet for the part says it is UL508 recognized. My guess is if you hunt down the UL recognition for this part it might tell you what the SCCR is.

 

[petersonra]

I think UL would assign a default rating of 5 kA to such a device. If you need more than that you would need to find a device with a higher rating. You could conceivably use the same 3 phase device previously used, but only use one phase of it.

 

[StarCat]

Don't you typically control resistance heat with an SCR Power Controller device when you want something other than contactors doing the switching? They are specifically made for this duty and have the necessary ratings and durability for such.

 

[petersonra]

Don't you typically control resistance heat with an SCR Power Controller device when you want something other than contactors doing the switching? They are specifically made for this duty and have the necessary ratings and durability for such.

That is exactly what he has

 

[MFS-PDX-313]

I think UL would assign a default rating of 5 kA to such a device. If you need more than that you would need to find a device with a higher rating.

Those are both the problems that I'm dealing with. The customer is demanding that the equipment have a 10kA SCCR. My project manager doesn't want to use something different (unless I can prove it out). I can't seem to find what the default SCCR rating is for an SSR. I have emailed my local UL rep to find out. I'm just kind of waiting to hear back from them so I can use the single-phase SSR that I found that has a 100kA SCCR rating when used with the proper fusing.

 

[petersonra]

Those are both the problems that I'm dealing with. The customer is demanding that the equipment have a 10kA SCCR. My project manager doesn't want to use something different (unless I can prove it out). I can't seem to find what the default SCCR rating is for an SSR. I have emailed my local UL rep to find out. I'm just kind of waiting to hear back from them so I can use the single-phase SSR that I found that has a 100kA SCCR rating when used with the proper fusing.

the cost to change is probably not that bad compared to all the screwing around you are doing.

 

[StarCat]

Ahh, I see the Part Nmber now.

 

[MFS-PDX-313]

the cost to change is probably not that bad compared to all the screwing around you are doing.

Maybe you've never dealt with a bull-headed project manager...

 

[MFS-PDX-313]

Also, here is the response I got from tech support at IDEC:


This is the reply I got from the Product Manager regarding the SCCR for relays.

“No we do not have and we do not need SCCR ratings on the relays.

Please note that relays are control circuit devices and do not need SCCR ratings



Short Circuit Current Ratings (SCCR) And Control Circuits

Question: Do the components in a control circuit have a short circuit current rating?

Answer: UL and NEC rules define which components in a control panel require a short circuit current rating.

Control circuit devices, such as pilot lights, push buttons, etc,do not have an SCCR, nor are they required per the NEC or UL 508A.

UL 508A September 2009 and NEC 2008 both talk about what is required to have an SCCR rating, and what is not.

The NEC 2008 (NFPA 70), 409.110 states: "Exception to (3)Short-circuit current rating markings are not required for industrial control panels containing only control circuits.." When you read and apply this to a panel when you have a mix of power and control circuits, the rational of not having short circuit ratings on control circuit devices becomes clearer.

UL 508A SB4.2.1 states "All power circuit components, including disconnect switches, branch circuit protection devices, branch circuit fuse holders, load controllers, motor overload relays, terminal blocks, and bus bars, shall have a short circuit current rating expressed in amperes or kiloamperes and voltage."

UL 508A does not require SCCR for control devices."

 

[jim dungar]

Also, here is the response I got from tech support at IDEC:


This is the reply I got from the Product Manager regarding the SCCR for relays.

“No we do not have and we do not need SCCR ratings on the relays.

Please note that relays are control circuit devices and do not need SCCR ratings

It appears the manufacturer does not suggest using this particular relay to control the power circuit as you are intending.

Many people misapply switching devices, like relays and small limit switches, because they think the only thing that matters is the 'Amp', or continuous, rating of the device. They forget or do not know that the make and break ratings, the load PF, and the duty cycle also need to be considered.

 

[petersonra]

It appears the manufacturer does not suggest using this particular relay to control the power circuit as you are intending.

Many people misapply switching devices, like relays and small limit switches, because they think the only thing that matters is the 'Amp', or continuous, rating of the device. They forget or do not know that the make and break ratings, the load PF, and the duty cycle also need to be considered.

This is a 30 Amp HP rated SSR. It is not a control relay. It is a power relay.

 

[Jraef]

This is a 30 Amp HP rated SSR. It is not a control relay. It is a power relay.

Yep. Although they are correct in their statement about control relays not needing to have an SCCR, what they are NOT correct on is that this device (THEIR device) is NOT a control relay, is is a POWER CONTROLLER. It says so right on the product data and in their UL listing for it.

NMFT2.E194577 - Motor Controllers, Mechanically Operated and Solid-state - Component

So they are either not paying attention to the exact question you are asking, or they are ignoramuses (ignorami?), or they just don't care to look into it any further for you (or any combination of the above).

"UL Recognized" by the way also means you cannot use this device stand-alone, it MUST be used with some other device or as part of a UL listed "system". I would venture to say that it might be that it must be used with fuses or a contactor, but Idec would have to tell you that.