new showere and 45a mcb (MK) crackling sound problem

[gibbad]

Hi all,

I have recently installed a 9.5kw triton shower. The property used to have a 7.5kw shower fitted with 6mm t&e cable, isolation switch and a 32a mcb to the consumer unit. The consumer unit is mk make with an isolation switch for main power and 2 rcd 80a 30ma which i think is split system with 2 mcb (lights) then 6 other mcbs (main electrics,etc)

I have rewired the existing set up with 10mm t&E cable and upgraded the fuse to a 45a mcb.

Everything seemed fine and the shower works fine however upon first starting and during the use of the shower the consumer unit (no problems shower end) makes a crackling/hissing sound which comes and goes.

Is this a problem that I need to investigate or is it normal to hear this.

Any help greatly appreciated.

 

[ban-all-sheds]

I have rewired the existing set up with 10mm t&E cable and upgraded the fuse to a 45a mcb.

On the RCD side, I hope...

Everything seemed fine and the shower works fine however upon first starting and during the use of the shower the consumer unit (no problems shower end) makes a crackling/hissing sound which comes and goes.

Is this a problem that I need to investigate

Yes - ASAP!!

or is it normal to hear this.

Not AFAIK.

Check that the cable and busbar screws are nice and tight - 40A is a lot of current to be passing through dodgy contacts.

 

[gibbad]

??

I replaced everything that the original circuit had from shower thru to mcb.

I basically changed wiring and mcb. I have not done anything different to the original set up.

 

[gibbad]

further to above. Does the earth cable being contected near the incoming master fuse earth connection block make a difference as the other mcbs earths are on a separate connection block.

does it matter?

 

[mapj1]

Its not the earth !
Fizzing noises, like the smell of burning that will follow if you don't fix it, indicate a loose connection. Check all the contacts and screws, not just the new ones, you may have disturbed one that was not tight before, but just happened to be pushed in and contacting. As an outside chance it could be the MCB itself, but I doubt it. A length of rubber tube or insulated pipe may make a simple stethascope that will help you narrow it down.
Do be very very careful, this sounds like it has the potential to become most unpleasant.
regards M..

 

[Gus220]

Hi

If you have test tightened all the screws and not found one lose then:

remove the busbar, loosen the screws some more and then refit the busbar. It is possible that the screws are tight but the clamp in the RCD/ctt breakers have missed the busbar. The sound you are hearing is arcing across this gap. Please check asap.

Gus

 

[gibbad]

someone at work has told me that the mcb's should be in order of ampage along the bus bar however somebody else has said it doesn't matter.
My current cofiguration is as follows:

45a, 16a, 32a, 32a, 32a, then elcb, then isolation switch.

Please advise,
I will go home and implement these suggestions and then report back in the morning.

 

[spence_spark]

its definately advisable to have the mcb's in descending order form the main isolator switch if at all possible

 

[ban-all-sheds]

??

I replaced everything that the original circuit had from shower thru to mcb.

I basically changed wiring and mcb. I have not done anything different to the original set up.

Not suggesting you have - just possibly not tightened things up properly. The thing with 10mm² cable is that the strands can sometimes "settle" after you've first screwed them in, and a few days later you can find that the terminal screw can be tightened a bit more.

someone at work has told me that the mcb's should be in order of ampage along the bus bar however somebody else has said it doesn't matter.
My current cofiguration is as follows:

45a, 16a, 32a, 32a, 32a, then elcb, then isolation switch.

Wrong order - the higher rated MCBs should be nearer the main switch/RCD.

 

[gibbad]

I have followed the advise given so far and moved mcbs and tightened,checked fittings.

The initial noise now comes from the power company main fuse before the meter for a few seconds upon starting up shower, then the noise moves to a buzzing, humming sound from the MCb itself until about 30-45 seconds when the noise then stops. There appears to be no noticable affects at the shower end though.

My partner has informed me this morning that the sound did not occur.
?? is the power consumption of my consumer board exceeding the inital power company supply when all appliances are using power at once. ie late evening more demand than 7am. therefore the mcb is straining to get full power.?


thanks for advise so far.

 

[mapj1]

If it really is the company fuse working loose in its holder (they are held by screw clamps internally), it is a case of waiting until you are sure it really is, then calling the REC/DNO out to look at it (once you have negoitated the "have a nice day, what colour would you like your bill" brigade). A slight hum from a magnetic circuit breaker near its full rating is normal, its the magnetic field from the actuator coils vibrating the turns a bit. BUT a fizzing, crackling or sparking noise is definately not, and should be ruled out.
good luck, M.

 

[gibbad]

I have been told that if an earth sleeve exposed any bare earth then this would contribute.

if so then I will double check all the connections to verify.

advice welcome.

 

[mapj1]

I have been told that if an earth sleeve exposed any bare earth then this would contribute.

that is I'm afraid, just rubbish.

I'd be very surprised if anyone telling you this was a proper electrician. The plastic insulation is there to protect the copper against damage, and accidental contact. In normal use very little current flows down the earth wire in any case, certainly not enough to cause any magneto acoustic effects.
Of course having wires well sleeved is a good thing, both from a neatness and safety perspective, but sleeved earths or not will not affect one iota the noises from the installation, unless its so badly done that bare wires actually touch live to earth, and then you get a very noticeable one-off noise (a loud 'bang' sort of noise actually, accompanied by a transient surge in the local photon flux. )
Once the ears recover and the eyes have stopped blinking you can than identify where the fault used to be by the missing bits of wire.

However, assuming your wiring is not a total bird nest, then this earth sleeving advice is a green-yellow herring.
regards,
M.

 

[gibbad]

A BIG THANK YOU FOR EVERYONES HELP.

I have come to the conclusion that all the MCb's are as per the recommendation in size order along the busbar, I am confident that at present all the screws, etc are tight (although will double check at end of week)

The noise , Humming??, from the 45a mcb only occurs upon start up of shower although shower works ok, possibly amount of electric current being demanded at first start.

i will let the matter lie and hope that its sorted now. At the weekend my father will be visiting me and he is very experienced with electrical appliances, ex building person, and i am sure if he's concerned he'll call in a few favours and get it sorted.

if anyones got any further advice upon the matter let me know.

Thanks

 

[ban-all-sheds]

Is there any smell of burning, or an ozone smell, coming from the main fuse?