Help!!!! Metrel Mi3000 tester problem

[Deleted member 26818]

My name's not Tosh?

 

[a-z electrics]

Well I stand to be corrected as I dont have a full manual (the quick guide doesn't mention it) but I have never had trouble testing type B RCDs.
How would the type affect the earth leakage trip though?

 

[davesparks]

Well I stand to be corrected as I dont have a full manual (the quick guide doesn't mention it) but I have never had trouble testing type B RCDs.
How would the type affect the earth leakage trip though?

It's not an earth leakage trip, it's a residual current trip.
The type denotes the various types of residual current that the RCD will operate with. type B RCDs are designed to cope with residual currents with a DC component, and will need testing differently to a type AC RCD. Whilst it will trip on a normal RCD test you will not be testing it properly.

The fact that a type B RCD is designed to ignore DC currents might explain why it trips on an non-trip loop test since testers use DC to saturate the coil of a normal RCD to prevent it tripping.

 

[a-z electrics]

It's not an earth leakage trip, it's a residual current trip.
The type denotes the various types of residual current that the RCD will operate with. type B RCDs are designed to cope with residual currents with a DC component, and will need testing differently to a type AC RCD. Whilst it will trip on a normal RCD test you will not be testing it properly.

The fact that a type B RCD is designed to ignore DC currents might explain why it trips on an non-trip loop test since testers use DC to saturate the coil of a normal RCD to prevent it tripping.

OK thanks for that.. I'm getting confused with the type B fuse curve, as in a type B rcbo.
I've found the full Metrel manual now and it doesn't actually mention type B, just type AC (sine wave) and type A (dc pulse) which are the test currents. It only differentiates between two types of RCD to test - G (general) and S (delayed). I've just checked a control gear RCD and the leaflet states its for AC or A. So I don't know what a type B RCD is then? Either way, a domestic RCD will surely be an AC but I can understand now why the question was asked..
Wishing all on the forum a very Merry Christmas!

 

[davesparks]

AC and A are the types of the RCD that it can test, the other type being B
Type B RCDs are rarely required and rather expensive, and most multifunction testers don't cater for them.
I've been looking at megger recently with a view to replace my mft and the only one which does type B RCD is the top of the range one (which I have no need for)

 

[Deleted member 26818]

Type B RCBOs are used where there is PV.
So they will become more common place, as more homes get PV.
I believe also, that they are required for vehicle charging points?

 

[davesparks]

They are only required when the DC residual current component exceeds a certain value (6mA springs to mind)
If the PV equipment or charging unit has built in protection to prevent a DC residual current then a type A RCD is ok.

And that's the extent of my knowledge on these areas so can't go in to any more detail