RCBO on TT earthing is it safe

[Yr ys]

Is it safe to use single pole RCBOs on a TT earthing system without an rcd and just a double pole breaker?

What would the max allowable earth resistance be to cut out a earth to neutral fault?

 

[Deleted member 26818]

Yes it is safe.
Maximum resistance for 30mA RCD/RCBO is 1667 ohms.
Not sure what you mean by ‘cut out a earth to neutral fault’.

 

[Yr ys]

Thank you for your kind reply.

Sorry I meant because the rcbos are single pole it wouldn't disconnect the neutral due to a earth to neutral fault. It would detect it however and disconnect the phase only. Am I right? And a double pole isolation is good enough no need for an rcd?

 

[Deleted member 26818]

Thank you for your kind reply.

Sorry I meant because the rcbos are single pole it wouldn't disconnect the neutral due to a earth to neutral fault. It would detect it however and disconnect the phase only. Am I right? And a double pole isolation is good enough no need for an rcd?

Yes, that’s right.

 

[Yr ys]

Thank you kindly.

 

[Strima]

Double check manufacturers instructions if using RCBOs on a TT system as some state that certain types are not suitable for use such as Schneider single pole devices.

You do need a method of isolating all live conductors on a TT system but this can be done at source by one single pole device, however I personally would install double pole devices on TT systems on all final circuits as there could be quite a large potential difference between neutral and earth and a double pole device would allow you to safely isolate both live conductors on a final circuit.

 

[HappyHippyDad]

Hi everyone,
I would like to rob a bank, as long as I don't hurt anyone would that be ok?
If just one of you random strangers says 'yes' then I believe that would suffice for me to go ahead.
Many thanks.

 

[HappyHippyDad]

Yes, that’s right.

You are of course right Spin, but I couldn't resist with the above.

 

[HappyHippyDad]

Is it safe to use single pole RCBOs on a TT earthing system without an rcd and just a double pole breaker?

What would the max allowable earth resistance be to cut out a earth to neutral fault?

No offence to you either chap, just having a giggle over a late lunch

 

[Yr ys]

Double check manufacturers instructions if using RCBOs on a TT system as some state that certain types are not suitable for use such as Schneider single pole devices.

You do need a method of isolating all live conductors on a TT system but this can be done at source by one single pole device, however I personally would install double pole devices on TT systems on all final circuits as there could be quite a large potential difference between neutral and earth and a double pole device would allow you to safely isolate both live conductors on a final circuit.

Hi and thanks for your kind reply

You mean isolate all circuits with one double pole breaker right?

 

[davesparks]

Thank you for your kind reply.

Sorry I meant because the rcbos are single pole it wouldn't disconnect the neutral due to a earth to neutral fault. It would detect it however and disconnect the phase only. Am I right? And a double pole isolation is good enough no need for an rcd?

This problem is present with SP RCBOs regardless of which earthing system is in use.
The RCBO will detect the fault on the N and disconnect the L.

 

[andyb]

Hi everyone,
I would like to rob a bank, as long as I don't hurt anyone would that be ok?
If just one of you random strangers says 'yes' then I believe that would suffice for me to go ahead.
Many thanks.

Yes.

 

[Yr ys]

All good.

This problem is present with SP RCBOs regardless of which earthing system is in use.
The RCBO will detect the fault on the N and disconnect the L.

Why do some manufacturers specifically say do not use on TT systems?

 

[Yr ys]

Yes.

No

 

[Strima]

All good.


Why do some manufacturers specifically say do not use on TT systems?

Because they're the manufacturers and they can say that.

 

[happysteve]

It's worth mentioning that some RCBOs switch their neutral also (e.g. SBS, Wylex and Crabtree).

 

[davesparks]

All good.


Why do some manufacturers specifically say do not use on TT systems?

I couldn't say for certain, presumably it is to cover their arses in case of issues, also they probably sell the same devices in country's where it is not allowed and its cheaper to make all the instruction sheets the same than print a different one for every country.

Also some manufacturers specify lower Zs limits than the often quoted 1667.

 

[TobyJones]

Hi everyone,
I would like to rob a bank, as long as I don't hurt anyone would that be ok?
If just one of you random strangers says 'yes' then I believe that would suffice for me to go ahead.
Many thanks.

How did the robbery go, out of prison yet?