what ohms trips rcbo's

[wattsup]

ball park figure:
The actual number is beyond my limited old brain
Insulation res. test n&e would trip (set 500v) rsbo/rcd
What is the threshold / trip ...not trip, ohms reading on tester
I guess some manufacturers may differ slightly, but there must be an inbetweeny?
In the old days, n&e faults were not so important (re-tripping breakers) cos of course no rcd's/rcbo's to worry about...
However, the 'board' would not connect a new supply with a 'low reading' Live Earth or Neutral Earth
Many times low readings were due to damp conditions, new builds. damp plaster etc. Nevertheless the board would not connect until 'their megger' said ok....

 

[jaresquire]

Depends on trip current of RCBO but as a guide 230V/30mA =7.7k ohms

 

[wattsup]

8000 ohms ish at 30mA ?

 

[telectrix]

ish...

 

[JUD]

A 30mA RCD/RCBO could trip anywhere between 16 - 30mA so in theory anything over 14.4kΩ (230V ÷ 16mA = 14375Ω) and it shouldn't trip. The regs however require 1MΩ and anything under 2MΩ requires further investigation.

 

[Guest123]

8000 ohms ish at 30mA ?

I'd go a bit higher (Bruce Forsyth style) as a correctly functioning 30mA device will give up at around 24mA....9500ohms.

Anything below 2Mohms requires further investigation anyway.

 

[netblindpaul]

Eh?
How can Ohms trip an rcbo, it's not possible.
It is the current flowing that will trip a protective device NOT the resistance.
What the heck are you lot on about?

 

[pushrod]

If you have a low enough resistance then 230 Volts will drive a current capable of tripping an rcd - somewhere between 16mA and 30mA for a common 30mA device (often about 22)
So R = 230/0.03A (or 0.022ishA)

 

[topquark]

Eh?
How can Ohms trip an rcbo, it's not possible.
It is the current flowing that will trip a protective device NOT the resistance.
What the heck are you lot on about?

Must admit it confused the heck out of me yesterday (I thought better of it and deleted the someone tongue in cheek post I posted).

 

[Des 56]

Well.I didn't contribute,because I just cant do the maths :26:

 

[daiplayer]

confused me when first looking too....lol

 

[ColinJones]

Depends where the resistor is placed.

7-8K should be low enough to trip an RCD if it's between Live and Earth. I'll let someone else work out how low it has to be to trip the RDC if it's between Neutral and Earth

 

[ackbarthestar]

Try this link it maybe able to help

RCD - DIYWiki

The earth reference wire references the neutral so when an unexpected current/voltage spikes flows causes a change in voltage between the earth and neutral the RCD will trip automatically.
As you read they were initially designed to pick up failed neutral faults on pme systems faults

 

[ColinJones]

This description of how they work also worth a read...

How RCDs work (residual current device circuit breakers): Explain that stuff!

Basically the current flowing in live and neutral create oposing magnetic fields in a torroid in the RCD. If they are identical the net result is no magnetic field. If there is a missmatch the resulting magnetic field is picked up in a coil and used to operate the relay that disconnects the power.

The problem with calculating an equivalent resistance that will trip out the RCD if placed between neutral and earth comes about because the neutral point of an supply is often connected to earth.

 

[ackbarthestar]

This description of how they work also worth a read...

How RCDs work (residual current device circuit breakers): Explain that stuff!

Basically the current flowing in live and neutral create oposing magnetic fields in a torroid in the RCD. If they are identical the net result is no magnetic field. If there is a missmatch the resulting magnetic field is picked up in a coil and used to operate the relay that disconnects the power.

The problem with calculating an equivalent resistance that will trip out the RCD if placed between neutral and earth comes about because the neutral point of an supply is often connected to earth.

Yes, I agree, but that doesn't explain why a non-energized RCD will sometimes trip when another circuit is activated... If you see what I mean

 

[daiplayer]

is that because of voltages present on the neutral bar , therefore present on all circiuts connected to the neutral bar . even when off. ? ,,,,,

Sent from my GT-S5830 using Tapatalk

 

[ackbarthestar]

is that because of voltages present on the neutral bar , therefore present on all circiuts connected to the neutral bar . even when off. ? ,,,,,

Sent from my GT-S5830 using Tapatalk

Yep, its the nature of the design of some RCBOs, a sudden surge of voltage on an independent circuit where the neutrals are separated between two dbs causes a momentary unbalance between the earth and neutral.

 

[wattsup]

Thanks guys, some interesting points
i guess some rcbo's / rcd's are more sensitive than others
A bit like people really -;

 

[ColinJones]

Yes, I agree, but that doesn't explain why a non-energized RCD will sometimes trip when another circuit is activated... If you see what I mean

In an ideal world Live and Neutral would follow exactly the same path so that any influence from another circuit would effect both equally. However that's not possible.

It's also not unknown for people to "borrow" a neutral from one circuit to use on another. That can cause the neutral current on circuit 1 not to match the live current on curcuit 1 ..and trip out the RCD.

 

[daiplayer]

In an ideal world Live and Neutral would follow exactly the same path so that any influence from another circuit would effect both equally. However that's not possible.

It's also not unknown for people to "borrow" a neutral from one circuit to use on another. That can cause the neutral current on circuit 1 not to match the live current on curcuit 1 ..and trip out the RCD.

almost garanteed on thw landing light. lol

Sent from my GT-S5830 using Tapatalk

 

[davie spark]

ball park figure:
The actual number is beyond my limited old brain
Insulation res. test n&e would trip (set 500v) rsbo/rcd
What is the threshold / trip ...not trip, ohms reading on tester
I guess some manufacturers may differ slightly, but there must be an inbetweeny?
In the old days, n&e faults were not so important (re-tripping breakers) cos of course no rcd's/rcbo's to worry about...
However, the 'board' would not connect a new supply with a 'low reading' Live Earth or Neutral Earth
Many times low readings were due to damp conditions, new builds. damp plaster etc. Nevertheless the board would not connect until 'their megger' said ok....

The actual figure is 7666.66 ohms but that's at bang on 230 volts, if the voltage was 240 (which it's usually nearer) it would be 8000 ohms as someone else has indicated.