Thread: BS4 electrical woes

Old BS4 with newish 1/2 HP SP motor trips RCD.

Over the last year it has trip the RCD maybe every 3-4 months - could never work out why because it wouldn't do it again.

This morning it ran for about 10 minutes (cut couple of pieces of angle) and then it tripped the RCD.
Then it ran for about 30 secs tripped again.
Now it trips every time motor switched on.

Meggered motor - fine, cap is fine.
Remove Belt - motor runs fine.
Put belt back on - trips.
Removed blade/band, (drive wheel moves freely) still trips
Can put a decent load on motor pulley with piece of wood - runs fine.

Suggestions welcome.

Does it have a earth wire connected, I know mine hasn't from factory.
Since I have run coolant for at least 12 years at least, and knew about the earth then, I should really put one on it, lol.
Mine isn't a BS model, but a similar 100x115mm saw.

Sent from my 5007U using Tapatalk

Fault in the centrifugal switch?

Sent from my SM-G973F using Tapatalk

The switch it came with was obviously not original and I replaced it with a no-volt switch with an earth connection inside the switch box and one at the motor.

ARRGHHHH - the firkin thing is now working!

I suspect it might be related to where it has been sometimes parked ie under a shed leak!
Maytbe running it without the belt allowed it to warm up - dry out?
Doesn't really explain why it ran without belt but tripped with the belt on?

No centrifugal switch by the sounds it makes.

If your consumer mains lags a bit it can create the small amount of imbalance required for operation of a residual current breaker (keep in mind a serviceable RCD should operate at 30mA).

And this morning its tripped again.

Cut one 30x30x3 mm piece of angle and then trips the RCD.

Still runs fine without the belt.
Trips with or without blade/band.

Hi Bob, Guys,

A couple of things, if the motor is vented stripping and cleaning the interior would be a good idea. Also check that non of the windings are loose or damaged anywhere. I don't recall whether you said that it had a centrifugal switch or if it had dual capacitors. Anyway electrical connections can loosen and cause current peaks.

One of the issues that I discovered after using mine for some time was very fine swarf got into the switch and caused the breakers to trip intermittently. I've cured this problem by taping a plastic cover over the whole switch. I also brush the fine swarf away regularly, it surprises me just how much accumulates on there.

The new switches have a built in flexible plastic shield and a built in no volt relay otherwise they are an almost direct replacement for the original one.

HTH.

Thanks BJ,

Originally Posted by BaronJ

Hi Bob, Guys,
A couple of things, if the motor is vented stripping and cleaning the interior would be a good idea. Also check that non of the windings are loose or damaged anywhere. I don't recall whether you said that it had a centrifugal switch or if it had dual capacitors. Anyway electrical connections can loosen and cause current peaks.

It's not a vented motor but it is going to be my next steps.

It only has one cap, but I can't hear a centrifugal switch re-engaging on shutdown.

Like I said it has occasionally been parked under a roof leak, There are a few rust spots on the steel pulley to confirm this. There's no water and there does not look like there's been any water inside the motor connection box (also and IP66 rated box.

One of the issues that I discovered after using mine for some time was very fine swarf got into the switch and caused the breakers to trip intermittently. I've cured this problem by taping a plastic cover over the whole switch. I also brush the fine swarf away regularly, it surprises me just how much accumulates on there.

The new switches have a built in flexible plastic shield and a built in no volt relay otherwise they are an almost direct replacement for the original one.

I doubt its the switch as the Switch is inside an IP66 rated enclosure. If it was the switch it should trip even without the belt. I've had the motor running with no belt for more than 15 continuous minutes without tripping.

BTW lube pump has been completely disconnected for all these tests.

Is the RCD a separate device, and not a combined CB / RCD ?

And thinking outside the square, is the belt a conductive belt ? Could it be the bridge to earth for the fault ?

Originally Posted by droog

Is the RCD a separate device, and not a combined CB / RCD ?

The RCD is built into the shed's main switch.

And thinking outside the square, is the belt a conductive belt ? Could it be the bridge to earth for the fault ?

Humm , , , , Will have to look into that.

Put the belt on it and put an AC clamp on it. Sounds more like it’s tripping on overload than leakage.

The BS is on a 10A GPO circuit with a 16A CB but that CB is not tripping. What’s tripping is the main shed switch that has an RCD built into it.

I have an ammeter/power meter so will take some readings tomorrow.

How big is the overload on the RCD/MCB?

30mA