Discuss BANG! in the Electrical Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

That bit has bothered me about the Hager (and some others), the connection is directly to the main switch, no local protection.

Some others dedicate one of the spaces for a MCB (45/50A) just for the SPD, but with others like Hager, you are wholly reliant upon the DNO fuse. In this case it was a 60A (now 80A).

So need to involve the DNO (I did have a suitable fuse btw, but not up to me to change it!)
 
Some manufacturers are happy to omit protection if the suppliers fuse is below a certain rating such as Wylex shown below.

BANG! Capture.JPG - EletriciansForums.net
 
Hager’s type 2 spd has internal overcurrent protection
Taken from their technical WhatsApp from a question I asked about it

Good Morning Ian, the SPD fitted within our consumer units have built over current protection therefore an MCB isn't required for protection of the device.
They are self protecting up to 100A.
[automerge]1592229656[/automerge]
If anyone has WhatsApp then add this number , it’s Hager’s technical support
07778 161 000
 
Last edited:
Usually, if or when the MOV's inside an SPD break down and fail they pass enough current to cause a clean disconnect of the upstream overcurrent protection whether it be a fuse or an MCB. They're basically a diode with a high forward voltage and if the surge has sufficient energy the junction will break down and may become fully conductive at a voltage below the normal supply voltage. They often have some type of internal fusing but it's good practice and often in the manufacturers instructions to use a dedicated fuse or MCB as protection.

That particular unit doesn't look like any MOV failure I've seen before. I'd strongly suspect the there was a flash across the L+N caused by the ingress of the pollution you noticed.

Incidentally, what size wiring was connected to it? We'd usually use 10mm but definately shouldn't be less than 6mm IMHO.
 
I stripped it down somewhat more, and there is a sticky substance all over the wires and parts of the internals - I assume something has been spilt from the shelf above recently - now I have been able to see it in the light of day!
Very soapy - the more I wash my hands the more soap suds I get!
It sounds anti covid19 induced.....automatic hand wash?

Caused by a basic short, then?
 
It sounds anti covid19 induced.....automatic hand wash?

Caused by a basic short, then?

Yeah, looks like it, I think the fact it was the spd is down to two things:

1) It's the most expensive part, therefore it's bound to happen there!

2) please refer to 1) again!

(sort of - see my thoughts below)

It turns out that they had a 5litre container of snowfoam (the sort of foam you use with a jetwash for car cleaning) which had leaked - but it was several days ago, and they thought they had cleaned it all up.

No idea any had gone in, and only associated it once I found the soapy residue.

Doesn't take away from the facts that it hadn't been installed properly, and if it had been protected by a local mcb, I suspect the damage would be much less.

Examining the RCBOs that were damaged (slightly) I think they suffered the same type of short due to the gunk, but tripped and cleared the faults, however by virtue of being protected by the dno fuse only, the spd was allowed to arc and burn for a long time.

No prior indication, the first time they became aware was stupid o'clock in the morning, arcs and flame sparking out of the cu. He ran round to our house, she got the kids out!
 
Now it’s getting down to who installed the Cu, cut corners and didn’t even do a tug test.

A loose connection could have caused a fire even without soapy bubbles

Yeah, it's actually quite a neat job to be fair, had I just looked at it I would have said it was a good job, now, I just want to go round there again and check all the connections!

I know mine are OK, and I checked all the screws for tightness, but didn't go too in-depth with the stuff I didn't touch.
 
That bit has bothered me about the Hager (and some others), the connection is directly to the main switch, no local protection.
It is obviously a bit of a trade-off as a MCB is another slot unusable for circuits, another cost, and (less obviously) has an impact on the SPD performance due to the series inductance the magnetic trip adds.

They typically have solder joint that is designed to disconnect if they get too hot which normally means a big lightning hit beyond their capacity. Not sure how pretty it would be with a open-PME style fault but I would like to think the manufacturers have t4ested for such conditions!

Gloop, probably not...
 
Looks like a slow drip of the gunge on the live, bubble and squeaking for quite a while before the short and bang. It seems a bit strange as to how much of the stuff got in and what exactly happened, with it being a few days previous to the actual occurrence. Expansion of the foam, gradual heat increase, maybe...but so long after?
 
It would be good if all manufacturers could change their terminals to prevent conductors from being inserted behind the clamp instead of in it.
Some terminals have a flat piece behind the clamp which travels with it to cover the hole when it is not open so you can't end up in this situation.

Even for the majority of us who do check every connection properly it is still very annoying when you find one which has gone behind the clamp, especially with the removable busbar normally found in domestic CUs.
 
Now it’s getting down to who installed the Cu, cut corners and didn’t even do a tug test.

A loose connection could have caused a fire even without soapy bubbles
Mistakes happen, everyone drops a clanger sometimes, and in our game that can mean a dangerous situation is created. This could be an innocent error by an otherwise conscientious electrician. I'm afraid it gets my back up when this sort of thing immediately results in an assumption that corners were cut, a cowboy, without any real evidence that this is the case. This could also be a manufacturer fitted unit, of course even manufacturer connections should be checked, but let he who is without sin cast the first stone.
[automerge]1592249547[/automerge]
It would be good if all manufacturers could change their terminals to prevent conductors from being inserted behind the clamp instead of in it.
Some terminals have a flat piece behind the clamp which travels with it to cover the hole when it is not open so you can't end up in this situation.

Even for the majority of us who do check every connection properly it is still very annoying when you find one which has gone behind the clamp, especially with the removable busbar normally found in domestic CUs.
Indeed, had a board which had been installed almost at ground level to add an MCB to recently, the whole busbar had to come out and the only way to make sure it was back correctly was with a mirror.
 
Indeed, had a board which had been installed almost at ground level to add an MCB to recently, the whole busbar had to come out and the only way to make sure it was back correctly was with a mirror.

I used to keep a mirror in my toolbox for doing this and for looking under floorboards and into voids, these days I use my phone camera or a wireless camera on the end of cable rods.
 
One of the reasons I like crabtree starbreaker is the plug in busbar. Never ever seen a burnt out busbar connection. The main switch terminals though are just as rubbish as all the rest!
 
Indeed, had a board which had been installed almost at ground level to add an MCB to recently, the whole busbar had to come out and the only way to make sure it was back correctly was with a mirror.
Sometimes you can't even get a mirror in. In these circumstances my method is:

(1) loosen all the terminals, push the screws in with a non-magnetic screwdriver so hopefully the cages are all at the back, in the right place

(2) put the bus bar in, hold it there with one hand

(3) starting at one end, tighten the furthest terminal until it nips the bus bar

(4) still holding on to the bus bar, loosen that one slightly, until the bus bar would drop if my hand wasn't holding it up

(5) go through all the terminals, confirm that tightening each of them will hold the bus bar up. So confirming that each terminal will actually grip the bus bar, meaning the cage is in the right place

(6) once all checked, tighten all the terminals, then torque them up.

Takes a while to do, and I kick myself if I drop the busbar at any point and have to start again! But it was the only way I could think of, of confirming that every terminal is correct, if you can't see any of them.
 
(I worry about my mental health at times)
... Am I part of the Truman show...
Coincidences youtubing 25kA testing yesterday.
Selling class J fuses !
(The arcing noises used to promote -Electrician things - does bug me)
 

Attachments

  • BANG! truman-show - EletriciansForums.net
    truman-show.png
    578.9 KB · Views: 32
Last edited:
I did......but I'm not going to claim that I've never made an error of similar magnitude in my 40 odd years as an electrician.
I
(2) put the bus bar in, hold it there with one hand

(3) starting at one end, tighten the furthest terminal until it nips the bus bar

(4) still holding on to the bus bar, loosen that one slightly, until the bus bar would drop if my hand wasn't holding it up
Also like when a new breaker is needed in say, a Wylex unit, you have to remove the bus bar altogether to fit it.
Similar to above but instead of (4), go along by nipping at the next breaker before slackening the previous, proving they're fastened one by one and holding in position. That way you're not depending on hand holding, it's constantly fixed.
 
Last edited:

Reply to BANG! in the Electrical Forum area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock