Touch Safe Fuse Holders

[AaronWood2008]

My company is implementing a safety policy stating that opening a "Touch Safe Fuse Holder" with voltage present is considered hot work and we need to get a "Hot Work Permit" to do so. We are not talking about under load but only having voltage and they are telling us that we need to disconnect all of the strings that are feeding the combiner or string inverter because safe touch fuse holders are not a means of disconnect. This seems like an insane amount of labor costs to simply check a fuse. Does anybody know of any documentation stating that opening a safe touch fuse holder with voltage present is a safe practice.

Thanks

 

[Carultch]

My company is implementing a safety policy stating that opening a "Touch Safe Fuse Holder" with voltage present is considered hot work and we need to get a "Hot Work Permit" to do so. We are not talking about under load but only having voltage and they are telling us that we need to disconnect all of the strings that are feeding the combiner or string inverter because safe touch fuse holders are not a means of disconnect. This seems like an insane amount of labor costs to simply check a fuse. Does anybody know of any documentation stating that opening a safe touch fuse holder with voltage present is a safe practice.

Thanks

How would that be any different than opening a voltage-energized MC4 connector, while not under load?

 

[petersonra]

Most of the so called touch safe fuse holders i have seen have access holes so you can check the fuse without opening it.

 

[ggunn]

My company is implementing a safety policy stating that opening a "Touch Safe Fuse Holder" with voltage present is considered hot work and we need to get a "Hot Work Permit" to do so. We are not talking about under load but only having voltage and they are telling us that we need to disconnect all of the strings that are feeding the combiner or string inverter because safe touch fuse holders are not a means of disconnect. This seems like an insane amount of labor costs to simply check a fuse. Does anybody know of any documentation stating that opening a safe touch fuse holder with voltage present is a safe practice.

Thanks

It sounds pretty stupid to me. Disconnecting bare energized conductors from a fuse block is a lot more hazardous than popping a fuse from a touch safe holder. What part of "touch safe" do they not comprehend?

 

[jaggedben]

How would that be any different than opening a voltage-energized MC4 connector, while not under load?

...or plugging one in.

 

[GoldDigger]

Contact arcing is usually less damaging than load break arcing.

 

[ggunn]

Contact arcing is usually less damaging than load break arcing.

What does that mean? Isn't all arcing load break arcing? If there is no load (no current flowing), how can there be arcing?

 

[Carultch]

What does that mean? Isn't all arcing load break arcing? If there is no load (no current flowing), how can there be arcing?

If there is a voltage difference that can ionize the air gap, there is arcing.

If you break the circuit NOT under load, there shouldn't be any air gap arcing. The resistance and corresponding voltage difference across the existing open portion of the circuit will be significantly greater than any resistance or voltage difference across the portion of the circuit you are in the middle of breaking. It is that "dangling resistor" problem from introductory circuits.

 

[jaggedben]

I can tell you from unfortunate experience that the arc on a PV source circuit is a hell of a lot longer lasting and more destructive if you disconnect while the inverter is running than if you disconnect after accidentally plugging the panel string into itself (i.e. short circuit). So if that's what Golddigger means he is 100% correct.

EDIT: I realize that's not exactly what he meant, since the short circuit is not exactly 'not under load'. But it's something similar.

 

[ggunn]

EDIT: I realize that's not exactly what he meant, since the short circuit is not exactly 'not under load'. But it's something similar.

Not exactly? Load is 1/R; a short circuit is maximum load.

 

[69gp]

poor quality pic. 277V

Found this on a job I inspected a few years ago. Who wants to replace this fuse? installed upside down with the feed on the top. you need to push the fuse in and hold while you close the holder. And yes the fuse can still be hot with the door open halfway.

 

[jaggedben]

Not exactly? Load is 1/R; a short circuit is maximum load.

I get what you say. I guess there's a couple things that are different about disconnecting a short circuit though. The short circuit does not flow at maximum power voltage, does it? Or does it?

My experience is that the arc is a lot less severe when disconnecting a short circuit. Maybe that's just because the voltage is lower, or maybe it's because as soon as you disconnect it there is no longer a load?

 

[GoldDigger]

I get what you say. I guess there's a couple things that are different about disconnecting a short circuit though. The short circuit does not flow at maximum power voltage, does it? Or does it?

My experience is that the arc is a lot less severe when disconnecting a short circuit. Maybe that's just because the voltage is lower, or maybe it's because as soon as you disconnect it there is no longer a load?

This is really hard for me to understand. I am not doubting your subjective experience, but unless the input of the load device has an inductive component (which it might!) I do not see why current flowing through the load will create a more persistent arc than current flowing through a short circuit.
The voltage will rise from zero (connected) to the full panel voltage so fast that it should not have any effect on arc formation. Unless there is a substantial capacitance associated with the panels! That might well be the difference.
In the short circuit case there will be an RC delay in the voltage rise whereas in the case of the CC or GTI load the voltage will already be at or near Vmp and can rise to Voc very quickly too.
I will settle on that as an explanation until theory or experiment proves me wrong.
A single shot storage scope attached to the two sides of the connection that is being broken should give a definitive answer.

 

[jaggedben]

This is really hard for me to understand. I am not doubting your subjective experience, but unless the input of the load device has an inductive component (which it might!) I do not see why current flowing through the load will create a more persistent arc than current flowing through a short circuit.

Well the 'load' is the inverter. And now that I think about it, my worst experience was with an isolated inverter, i.e. transformer model. (This was a few years ago now, and I've avoided anything similar since by being smarter.) Perhaps it's different with a non-isolated inverter?

You do have to pop the connectors on a short circuit very quickly to avoid damaging the connectors.

 

[AaronWood2008]

Thank you for all of the replys

Thank you for all of the replys

Somehow our safety manager thinks that it is safer to disconnect a string connector with voltage present then to open a fuse holder. To me it is insane but without some sort of documentation stating this is OK I'm stuck. There is probably no such documentation for something that is so blatant.

 

[AaronWood2008]

How would that be any different than opening a voltage-energized MC4 connector, while not under load?

I couldn't agree more

 

[Solar Peep]

I agree it's crazy, but your company is probably trying to follow OSHA requirements for EEW energized electrical work. Here is a chart that shows when you need a EEW permit and your PPE requirement. I know it doesn't make it any better but thought this could be helpful. The red text is when you need a EEW permit.:thumbsup:

 

[pv_n00b]

This might help. Get a cut sheet for the touch safe fuse holder in the equipment you are using. If the cut sheet says it has an IP code and the code is IP2X, where X can be any number, then it has been tested as finger safe to IEC 60529. If you want a UL standard then the fuse holder should be listed to UL 4248 for fuse holders and that standard requires that if it has an IP code that it be tested to IEC 60529.

The IP2X code indicates that you can't get a finger sized object in there. While you have to pay for IEC 60529 there is enough information reprinted on the internet that you can find information about the IP codes and what they mean. Here is one good reference from Eaton: Degrees of protection IP codes - Eaton

 

[pv_n00b]

View attachment 13509

poor quality pic. 277V

Found this on a job I inspected a few years ago. Who wants to replace this fuse? installed upside down with the feed on the top. you need to push the fuse in and hold while you close the holder. And yes the fuse can still be hot with the door open halfway.

You just can't fix stupid.

 

[SolarPro]

Well, in this case you could fix stupid by removing the fuse holders and turning them around. It's not rocket science. Even if this voids the product listing, the revised setup would be safer than the current setup—and safety is presumably the goal of product standards.

You could also complain to the OEM until they send you a new combiner box. Of course, based on their lax QA/QC, it wouldn't surprise me if they were no longer in business.