MCB tripping intermittently

[Buck Taylor]

Would fitting a PRV under the kitchen sink and setting it at 3.0 bar direct to the cold tap help?
There is also a PRV fitted going up to the header tank in the loft!

 

[Chuck]

Hi Mark/Chuck,
With the pump in the hum state I opened up another tap immediately and the MCB still tripped.

In your position, I'd try replacing motor's starting capacitor. You need to get the right type and size. Motor repair companies are relatively common so, if you're not sure what you're doing, check the Yellow Pages. They'll also be able to check the windings and bearings for you.

I now suspect that when the high demand outlets are used they are actually using the standing pressure to turn the impellor blades, which helps start the motor.

 

[Chuck]

Would fitting a PRV under the kitchen sink and setting it at 3.0 bar direct to the cold tap help?

I very much doubt it.

 

[Buck Taylor]

Definitely points to a failed/failing motor then.

What happens if you reset it and open a different tap?

Hi Mark,
It trips when either hot or cold tap is opened

 

[Mark K]

Hi Mark,
It trips when either hot or cold tap is opened

Yes, so once it's stalled (buzzing) it's going to trip, presuming you mean while it's buzzing.

Does it still work when other taps are opened from an off state?

 

[Buck Taylor]

Yes, so once it's stalled (buzzing) it's going to trip, presuming you mean while it's buzzing.

Does it still work when other taps are opened from an off state?

Yeah when buzzing and opening up another tap it trips the MCB.
Not sure what you mean about opening another tap from an off state?
The MCB has never tripped from opening any other tap in the house!

 

[Mark K]

Yeah when buzzing and opening up another tap it trips the MCB.
Not sure what you mean about opening another tap from an off state?
The MCB has never tripped from opening any other tap in the house!

I mean what you said..no other tap opening trips it.

As Chuck said it sounds like a motor and/or capacitor failing. The characteristics of the kitchen tap cause a higher current draw, which causes the breakdown and the motor stalls and won't start. Opening other taps doesn't cause the initial current draw, and hence heat, so the motor gets going.

I bet you can open the kitchen tap no problem if another tap is already running?

 

[Buck Taylor]

I mean what you said..no other tap opening trips it.

As Chuck said it sounds like a motor and/or capacitor failing. The characteristics of the kitchen tap cause a higher current draw, which causes the breakdown and the motor stalls and won't start. Opening other taps doesn't cause the initial current draw, and hence heat, so the motor gets going.

I bet you can open the kitchen tap no problem if another tap is already running?

Yeah opening the kitchen tap whilst the pump is running does not trip the MCB. Looked on
showerdoc.com for a replacement starting capacitor and it is sold out!!! Oh the joys I'll look for something compatible.

 

[Buck Taylor]

I mean what you said..no other tap opening trips it.

As Chuck said it sounds like a motor and/or capacitor failing. The characteristics of the kitchen tap cause a higher current draw, which causes the breakdown and the motor stalls and won't start. Opening other taps doesn't cause the initial current draw, and hence heat, so the motor gets going.

I bet you can open the kitchen tap no problem if another tap is already running?

Good morning gents,
The first time this has happened..... The tap in the downstairs toilet has now tripped the MCB, so does that now point more to the start capacitor?

 

[marvoni]

Do you have access to a clamp meter?



If you can beg, borrow or steal one for a few hours it will give you a definative answer.

It's a non-contact tester that measures current but you need to isolate the power whilst you clamp it around either the live wire or a neutral wire of the cable that supplies the pump.

If at any time the current being drawn by the pump exceeds the manufacturers stated maximum current you should replace the pump.

You could try replacing the capacitor but it's a long shot. Capacitor damage is visible in the majority of cases manifesting as a swolen or cracked casing or as burned terminations or other signs or arcing / overheating. Also, if the capacitor is faulty there's a high liklihood it was damaged due to another problem within the pump that caused high peak current or prolonged marginal over-current through it such as mechanical wear, bearing failure or scale build-up so it's more often than not a symptom rather than a root cause.