A period of time when a moderate amount of current can have an effect on a damaged cable via heat maybe?!?
16A MCB trips when tumble dryer is on
- Thread starter Jimbo
- Start date
A period of time when a moderate amount of current can have an effect on a damaged cable via heat maybe?!?
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I guess that's possible, but I've plugged the dryer into socket on both the radials from the MCB, and it trips on both. If there was a fault in the wiring, wouldn't it trip whether or not the dryer was running?
The cable is all surface mount and although I haven't inspected it at close range, it looks fine.
The one thing I haven't yet done due to time constraints is disconnect each radial in turn and run the dryer from one at a time. I'm hoping to get to that tomorrow.
Conceivably ('nothing is impossible'), but I struggle to think what sort of cable fault could result in that happening - reversibly and repeatedly.
Kind Regards, John
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I'd be tempted to temporarily wire the dryer directly into the MCB, removing all the other wiring - if you can do that safely.
I also wonder whether this (presumably) small enclosure with two MCBs is getting hot enough that this 16A MCB, which is going to get warm with 10A through it, is overheating. I'd consider temporarily running it with the front removed - if you can do that safely - and/or measure the temperature of the MCB as it runs.
I also wonder whether this (presumably) small enclosure with two MCBs is getting hot enough that this 16A MCB, which is going to get warm with 10A through it, is overheating. I'd consider temporarily running it with the front removed - if you can do that safely - and/or measure the temperature of the MCB as it runs.
I'm struggling to think what else it could be! If line(live) insulation damaged, could slight arching between line and earth occur after a short amount of time?
Why do that (and cut the plug off) when the dryer works ok with extension cable into a different socket outlet?
Front has been off since yesterday, not making any difference. The CU is one of these with a 30mA RCD and 16A mains MCB and 6A lighting MCB.
I could wire an extension cable directly into the MCB and plug the dryer into that. Can't put the dryer directly into the MCB as it's a sealed plug which I don't want to cut off as I might still be contacting them for a replacement if it's drawing significantly more than it should. However an extension cable will have multi-strand conductors and I'm a little nervous about putting multi-strand into the flat clamps you get on MCBs. I could tin it up I suppose!
I think that we're all struggling! What you suggest would almost certainly result in the RCD, not the MCB, tripping, at least sometimes - and we've been told that that has never happened. A fault such as you describe but resulting in an L-N short could conceivably do it - but the anatomy of T+E cable as such that it's virtually impossible to get an L-N short without also an L-E one (which would trip the RCD).
Kind Regards, John
I don't think stranded conductors are an issue but what is the CSA of your extension cable? It may be written on the reel housing of there is one, or the cable itself.
Even if unintentional, what you sugegsted was not as silly as you suggest. As I recently wrote, IF you measured the pd between L-in and L-out of the MCB (I also said with neutral, but that would not apply to a single-pole MCB!!), if current is flowing through the MCB, you will see a very small pd due to that current flowing through the (very small) internal impedance of the MCB. As I said, it would be a very small voltage - but it should be 'measurable', and any pd between those terminals would mean that current was flowing through it.
However, particularly given that it's Friday evening (and, co-incidentally, my birthday), please do feel free to have that drink!!
Kind Regards, John
I would be tempted to do that with the mcb OFF, if any unknown load was connected it will show up as a voltage reading, thats why I prefer my neon test lamp, as the brightness of the thing indicates the state of the load wiring, usefull on older installs
But the wiring hasn't changed in 9 years, and the MCB has never tripped until this problem started a few weeks ago!
The only other thing I haven't tried is to replace the RCD. It may be that it's faulty and not tripping before the MCB does. But given that I've run the dryer from both radials I'd have to have an earth or short fault on each radial, both of which started occurring at the same time!
Also I haven't checked whether the MCB in the main house CU, which feeds the garage, gets hot in the same way the garage MCB does. I assume it would if it's a current overload as they're rated the same.
I'm not the most experienced electrical guru but I will affirm that stranger things have happened!
How hot do people think a 16A MCB should get when passing 10A for tens of minutes?
Yes, check that; are they the same brand?
Yes, check that; are they the same brand?
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