240v sign casing

[sellers]

Just been to a call out to local takeaway where they had lost power to a sign behind the counter. Turned up, and a ballast had gone and taken out the fuse in the spur.

While I was there he mentioned another sign on the customers side that he thought he had had a shock off last week so he left it switched off. I put my tester in the earth of a local socket and onto the casing, and the voltage fluxuated starting at 10v-80-230. Undid the spur feeding that and the earth wasn't connected. Re-connected, casing earthed. Tried it on and it worked, now why wouldn't it trip the fuse or mcb? I take it the ballast is on its way out and starting to short to earth?

 

[Andy™]

I take it the ballast is on its way out and starting to short to earth?

most likely. happens all the time

 

[Larnacaman]

They just don't make Ballasts like they used too. Where an old type ballast would last in the most part, for the life of the fitting, these new electronic types last no time at all!!

Probably more efficient than the old type, but need for replacement seem to be far more frequent these days...

 

[Evans Electric]

It didn't trip or blow a fuse because ,I think you said , the earth wasn't connected .

 

[sellers]

It didn't trip or blow a fuse because ,I think you said , the earth wasn't connected .

yes, but when earth was connected and its switched on, no fuses blew?

 

[m4tty]

Could it be shorting to Earth when it heats up?

 

[Evans Electric]

I guess the fault current is now flowing down the earth wire then but not enough to blow a fuse . Is it a rewirable fuse ? An RCD would probably trip , I take it there isn't one ?

 

[sellers]

no, no rcd, but mcb's. Mustn't be enough fault current then.

 

[Andy™]

yes, but when earth was connected and its switched on, no fuses blew?

because the ballast limits the amount of power that can flow through the tube. and so limits the power that can flow to earthuntil it fails more and lets more through, then trips RCD's. and eventually a fuse

had a similar case a while back. SON lamp not working. live from ballast to lamp had shorted to earth. result: lamp didnt work, because it was taking the shortest path through earth, but limited so didnt blow fuse

 

[sellers]

everydays a school day, glad he got me to look at it while I was there, its in the food court of the local shopping centre in reach of the public and low enough for kids!