# Supplemental over current protection in control circuit



## Family guy (May 15, 2016)

I am trying to find a more cost efficient way to supply protection to a device that serves as remote start stop for grain bin site fans and heaters. It is not the start stop but they are contained in the device. I have been using an inline fuse holder and a midget fuse to provide protection but it is running a bit over $30 to go this route. In some cases there is need for two sets for one fan. Wondering what other methods and options are being used out there. I try to get a hold of another power source to energize device but sometimes it is not available. Thinking of switching to din rail and a din rail mounted miniature breaker, but not sure if there is a better option. 


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## John Valdes (May 17, 2007)

Why protect pilot devices? Your OCPD protects most everything and the control power is also fused or has a breaker.
Why would you want redundant protection. Or is the control circuit unprotected?
I'm not sure I understand?


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## Cow (Jan 16, 2008)

For control circuits tapped from larger circuits that leave the enclosure for remote start/stops, hoa's, etc we do as you mentioned. Either a midget fuse holder or din rail mount breaker, that is, if a separate control power source is not available.


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## Family guy (May 15, 2016)

Before I was hired by the company there was an installer that would run a 16 gauge cord from fan start stop to the control device ( pilot device). It was common for it to come off of L1 and L2 of the motor contactor which is usually right at the 100 amp mark. I did not see it right to continue use with the SO cable and switched to running sealtight and emt to go from motor to our device. Nor did I feel comfortable running power to energize the device without fusing down somewhere. I am also running 12 gauge thhn wire to make connection as that is my understanding when running a control circuit outside of box to a separate start stop I can carry that control circuit outside the box if I run 12 gauge and the breaker is not over 100 amps. I do utilize control fuse when available, And the pilot device is fused at one amp at the termination point. I am considering that power to energize the device to be outside of the control circuit because it’s function is to energize the device and not to stop stop the motor. When there is no control circuit fuse or the site is utility controlled so when they are controlled it would de-energize our box which is gathering data useful to the farmer I sometimes have to come straight off of the line side which is protected by a 100amp usually sometimes up to 125amp breaker.
I may be over thinking or thinking wrong but that is the way I am currently looking at it. I hope i can explain and not be too confusing.


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## micromind (Aug 11, 2007)

If you're using din rail, a flip-out fuse holder is less $$ than a breaker.


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## Family guy (May 15, 2016)

Cow said:


> For control circuits tapped from larger circuits that leave the enclosure for remote start/stops, hoa's, etc we do as you mentioned. Either a midget fuse holder or din rail mount breaker, that is, if a separate control power source is not available.













Looking at the table here I see that the breaker size is actually 60amp for a 12 gauge wire. Usually there is control circuit protection but thinking I was wrong in thinking it to be 100amp.



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## Flyingsod (Jul 11, 2013)

You Want decrease the cost from 30bucks? Is your time worth nothing? If your time is paid for I don’t see how spending less on misc materials at such a small amount is going to make up the difference from you spending more time installing it. 
Might also help people answer you if you’re not secretive about this mysterious “device”. What is it?


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## just the cowboy (Sep 4, 2013)

Use the flip out DIN mount fuses term strip type. They also have DIN mount flip switches that work good for inputs that need to be worked on without shutting down all power.


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## tates1882 (Sep 3, 2010)

Its about even for cost of an Eaton 1077 mini breaker and fuses with holder. The question is the aic that the supplementary protect will need to have. Most mini cbs carry a 10kA rating, fuses normally 50-200kA. I avoid fuses if possible, nothing like being one fuse short on Friday @ 505pm in the middle of nowhere on a service call.


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## splatz (May 23, 2015)

I had to double check I didn't remember these being expensive - the Eaton ones like $10 at Automation Direct. 

https://www.automationdirect.com/ad...pplementary_protectors_(0.5a-63a,_faz_series)


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## Family guy (May 15, 2016)

Flyingsod said:


> You Want decrease the cost from 30bucks? Is your time worth nothing? If your time is paid for I don’t see how spending less on misc materials at such a small amount is going to make up the difference from you spending more time installing it.
> Might also help people answer you if you’re not secretive about this mysterious “device”. What is it?
> 
> 
> Sent from my iPhone using Tapatalk




Device would be called Bin Manager. It has been a job first convincing that the cord was not code compliant and there is discussion about whether the fuses are needed. The boss man would like to say a set figure for all electrical installations per fan. Each bin gets one manager and each fan or heater gets one HOA to operate it via the intellifarms system. I am working in the direction to make things right (or what I would consider right). 
There is one other issue that is a bit fuzzy to me, and that is there is no ground needed nor provided for. I find myself going back and forth about using Liquid tight metallic flex or nonmetallic. When running from the fan to the bin. I have at this time been running metallic and terminating in a bell box running equipment ground. Then switching to emt to enter into manager (device). Some start stop at fans are nonmetallic and the bin manager is also nonmetallic, but where is the good low impedance ground if I run in nonmetallic flex or how is the metal bonded in sealtight if run in metallic. I have been debating using grounding bushings but is that sufficient for a length sometimes 10-12 feet to get from fan to bin. It would be nice not to have to use the bell box for a single fan. 
Just want to do it right without overkill if you know what I mean. And the farmer mentality ( of course not all) has been just make it work, and keep the cost down. 
Hope this helps explain part of the dilemma. Not to mention some jobs are 4 1/2 hours away from home going sight unseen has been an adventure. 


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## JRaef (Mar 23, 2009)

There is now a problem with using what is called "common control", wherein the control power is the same as the line voltage as in your "L1, L2" scenario mentioned above. Everything now needs to have an SCCR, but that only applies to devices operating at the main incoming line voltage. So if you have a control power transformer, only the primary fuses count, everything on the secondary is limited by the transformer. But if you use common control, now all of your pilot devices are operating at the line voltage and thereby require an SCCR commensurate with the Available Fault Current of the incoming source. No pilot devices actually carry an SCCR without current limiting fuses, such as Class CC, the type that are going to cost you the money. If you use the DIN rail mounted supplementary breakers, they are almost never good for more than 10kA, so you would likely need a fuse ahead of it anyway.


Once you go with a Control Power Transformer, that entire issue goes away; SCCR does not extend to the secondary side of a CPT. So assuming you have a secondary fuse on that CPT, you don't need another one even if the circuit leaves the enclosure.


If you have 120V "separate control", meaning coming from an external source, you need to have it disconnected by the starter disconnect (aux. contacts) and it should be fused (or supplementary breaker) at that point. Then again, no need for further OCPD from there.


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## Family guy (May 15, 2016)

JRaef said:


> There is now a problem with using what is called "common control", wherein the control power is the same as the line voltage as in your "L1, L2" scenario mentioned above. Everything now needs to have an SCCR, but that only applies to devices operating at the main incoming line voltage. So if you have a control power transformer, only the primary fuses count, everything on the secondary is limited by the transformer. But if you use common control, now all of your pilot devices are operating at the line voltage and thereby require an SCCR commensurate with the Available Fault Current of the incoming source. No pilot devices actually carry an SCCR without current limiting fuses, such as Class CC, the type that are going to cost you the money. If you use the DIN rail mounted supplementary breakers, they are almost never good for more than 10kA, so you would likely need a fuse ahead of it anyway.
> 
> 
> Once you go with a Control Power Transformer, that entire issue goes away; SCCR does not extend to the secondary side of a CPT. So assuming you have a secondary fuse on that CPT, you don't need another one even if the circuit leaves the enclosure.
> ...


Trying to catch what you are saying, and wondering if a normal breaker is rated for 10ka and the Eaton supplementary breaker is likewise 10ka why I would need fuses ahead of the breaker.
The following picture is an example as the contactor here is feed with a 80 amp breaker. I was at this point thinking to add a small piece of din rail and 2- 5 amp supplementary breakers. To provide power to my device and also become remote HOA for a fan and heater system on a grain bin.
.












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## tates1882 (Sep 3, 2010)

Family guy said:


> JRaef said:
> 
> 
> > There is now a problem with using what is called "common control", wherein the control power is the same as the line voltage as in your "L1, L2" scenario mentioned above. Everything now needs to have an SCCR, but that only applies to devices operating at the main incoming line voltage. So if you have a control power transformer, only the primary fuses count, everything on the secondary is limited by the transformer. But if you use common control, now all of your pilot devices are operating at the line voltage and thereby require an SCCR commensurate with the Available Fault Current of the incoming source. No pilot devices actually carry an SCCR without current limiting fuses, such as Class CC, the type that are going to cost you the money. If you use the DIN rail mounted supplementary breakers, they are almost never good for more than 10kA, so you would likely need a fuse ahead of it anyway.
> ...


 depending on the breaker they can be rated up to 200 AIC. Same for fuses. Fuses in front of a breaker can “increase” the AIC of the breaker in question. Most manufactures don’t do the fault testing with their competitors breakers but they will test with fuses to increase the over rating of the device. Google ul 508 and sccr, you’ll get tons of white papers from various manufactures that cover this very topic.


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## tates1882 (Sep 3, 2010)

Family guy said:


> JRaef said:
> 
> 
> > There is now a problem with using what is called "common control", wherein the control power is the same as the line voltage as in your "L1, L2" scenario mentioned above. Everything now needs to have an SCCR, but that only applies to devices operating at the main incoming line voltage. So if you have a control power transformer, only the primary fuses count, everything on the secondary is limited by the transformer. But if you use common control, now all of your pilot devices are operating at the line voltage and thereby require an SCCR commensurate with the Available Fault Current of the incoming source. No pilot devices actually carry an SCCR without current limiting fuses, such as Class CC, the type that are going to cost you the money. If you use the DIN rail mounted supplementary breakers, they are almost never good for more than 10kA, so you would likely need a fuse ahead of it anyway.
> ...


 also just FYI that pic shows a UR mark on the contactor, which means you can’t install this under the NEC. See article 409 nec


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