UK Plazma cutter causing SPD failure??

[Andy Y]

I've just had a potentially nasty issue involving a Burnt out, type 2 SPD. My customer has been using a small plasma cutter,
I don't have the exact details of the unit to hand, but it does plug in to a standard 13a socket outlet This is a new 100a single phase TT supply to a small commercial unit.
This was a very close call. The SPD, located directly next to the consumer mainswitch, had burnt out to such a degree, that it has (fortunately) taken out the fuse at the intake.
Is it possible, this cutter could produce enough transient voltage to create this issue?
I was led to believe, these devices should go open circuit when they fail.

 

[mainline]

Is it possible, this cutter could produce enough transient voltage to create this issue
I was led to believe, these devices should go open circuit when they fail.

The plasma cutter likely generated significant transients, causing the SPD to burn out instead of failing safely.

Didn't the SPD's MCB trip ?

 

[Andy Y]

The plasma cutter likely generated significant transients, causing the SPD to burn out instead of failing safely.

Didn't the SPD's MCB trip ?

No MCB on this Elucian board, thats how they are configured from the factory. I'm really unimpressed. According to the spec sheet they are rated at 300A, relying on the suppliers cut out for overload can't be right?
This cutter was apparently running for less than 60 seconds.

 

[Rockingit]

Sounds very odd to me. Are you sure that you’re not simply dealing with a poorly installed device and arcing from a loose termination?

 

[mainline]

No MCB on this Elucian board, thats how they are configured from the factory. I'm really unimpressed. According to the spec sheet they are rated at 300A, relying on the suppliers cut out for overload can't be right?
This cutter was apparently running for less than 60 seconds.

According to BS 7671, all SPDs shall be protected from over current, which can be done through the use of an MCB or internal fuse.

I would prefer a lower current mcb/fuse than rely on the cutout one.

It sounds to me like sales of single module spd's is first priority.

 

[mainline]

Sounds very odd to me. Are you sure that you’re not simply dealing with a poorly installed device and arcing from a loose termination?

A spd wouldn't normally carry any current.

 

[DPG]

A spd wouldn't normally carry any current.

I think he means a poor termination at the plasma cutter causing surges and therefore SPD issues. Although I don't want to put words into his mouth

 

[mainline]

I think he means a poor termination at the plasma cutter causing surges and therefore SPD issues. Although I don't want to put words into his mouth

Poor show of the spd whatever the reason was for the fail.

 

[DPG]

Poor show of the spd whatever the reason was for the fail.

Yep, true.

 

[UNG]

Never really looked indepth at SPD's but from what I have seen they are a one shot device usually requiring replacement of a plug in module or the complete device
So the question is once they have arreseted a surge how safe are these devices especially if there are welders, plasma cutters or other high current surge producing devices in use on a frequent basis, if there are issues with SPD's where there is a potential fire risk should they be installed in a separate enclosure

 

[Andy Y]

Thanks for the replies.
What really bothers me, is the fact that, say there's for instance, an old chappie who has a bit of a hobby workshop in his garage. He's tinkering around cutting a sheet, the main board is in the house. Being retired he has plenty of spare cash, and pops off on holiday early the next morning, completely unaware that thing is sitting there melting itself, for whatever reason.

 

[Andy Y]

Sounds very odd to me. Are you sure that you’re not simply dealing with a poorly installed device and arcing from a loose termination?

No, all correctly installed

 

[DPG]

SPDs, as with any switchgear etc are tested to stringent requirements and standards. Obviously occasionally something will go wrong, but I would say this is probably a freak thing.

 

[Andy Y]

SPDs, as with any switchgear etc are tested to stringent requirements and standards. Obviously occasionally something will go wrong, but I would say this is probably a freak thing.

I guess thats what it will be put down to. I'll have to wait & see what comes back from the manufacturer.
Something odd said by the fella sent out to replace the main fuse, (I had put in a temporary board by then)
'If it blows again, tell your sparky to move it over to another phase' Really?

 

[mainline]

Thanks for the replies.
What really bothers me, is the fact that, say there's for instance, an old chappie who has a bit of a hobby workshop in his garage. He's tinkering around cutting a sheet, the main board is in the house. Being retired he has plenty of spare cash, and pops off on holiday early the next morning, completely unaware that thing is sitting there melting itself, for whatever reason.

I’m guessing that in that type of single mod SPD that they dont have the soldered joint that melts if any real current for a period is drawn via the now shorted Mov.
You could put the garage on its own supply which is how it should have been done in the first place.

 

[Andy Y]

I’m guessing that in that type of single mod SPD that they dont have the soldered joint that melts if any real current for a period is drawn via the now shorted Mov.
You could put the garage on its own supply which is how it should have been done in the first place.

My mention of the garage was just a scenario. This install only has 1 board. I suspect you might be right about the soldered connection, but to my mind, that doesn't make it right.

 

[mainline]

My mention of the garage was just a scenario. This install only has 1 board. I suspect you might be right about the soldered connection, but to my mind, that doesn't make it right.

I suppose analysing the waveform when the plasma cutter is being used is the way forward.
If it's actually bad enough to cause damage to other equipment, then throw it in the bin.

 

[Andy Y]

I suppose analysing the waveform when the plasma cutter is being used is the way forward.
If it's actually bad enough to cause damage to other equipment, then throw it in the bin.

I guess so, it probably does belong
in the bin, I've looked it up & its a good old, generic, Chinese made contraption.

 

[Darkwood]

Are you sure their hasn't been a power surge from a local lightning strike, the plasma cutter may not be anything to do with it, such equipment should by design have its own suppression and smoothing circuitry to eliminate any unnacceptable interference on the power supply.

 

[Andy Y]

Are you sure their hasn't been a power surge from a local lightning strike, the plasma cutter may not be anything to do with it, such equipment should by design have its own suppression and smoothing circuitry to eliminate any unnacceptable interference on the power supply.

That's what I was thinking. It's not like this cutter was running for any great length of time either. Definitely no lightning strikes in the area though.

 

[UKMeterman]

Check the supply voltage is in spec, may need a voltage recorder.

 

[Andy Y]

Check the supply voltage is in spec, may need a voltage recorder.

Maybe there could be issues, it's part of a new build estate of small units

 

[UKMeterman]

TT supply, was it the L - N SPD that burnt or the L-E device?

 

[Andy Y]

TT supply, was it the L - N SPD that burnt or the L-E device?

It looked like the live connection side ( internally) burned against the neutral of the main switch