Replace MCBs with RCBOs
- Thread starter Graham.
- Start date
The Happy Builder
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What make is the consumer unit and MCBs?
Thanks for your replies, this is on a Square D Quickline 2 split board 7+7 all the existing Mcbs Rcobs are also Square D. The main incomer side of the board has a 100amp isol then 3 mcbs and 2 double pole rcobs, the second half of the board has a 100amp 30ma rcob incomer then 7 mcbs. Also installed is an Upfront 100amp 100ma S type RCB. I want to upgrade the main incomer side 3 mcbs ( 2 light circuits + 1 socket) to RCOBs.
Schnieder took over Square D and still supplies MCBS and single-pole RCOBs to fit.
Schnieder took over Square D and still supplies MCBS and single-pole RCOBs to fit.
Coloumb
Screwfix Select
A picture would really help. I think you are confusing RCBO's with RCD's. From what your saying it seems you want to protect the 2 light circuits + 1 socket ctts. with additional 30ma RCD protection as they are currently not protected? Does the socket circuit feed sockets likely to supply outside equipment? Is this board fairly old, it sounds a lot like a 16th edition board. Just because the regs have changed so now it's pretty much impossible to NOT fit RCD protection doesn't necessarily make older installations unsafe. I think you might be better off thinking about complete, all RCBO, board replacement anyway.
The Happy Builder
Screwfix Select
The upfront 100 mA S-type RCD is double pole, so the single pole 30 mA RCBOs are okay to use for additional protection, but a neutral fault on one of the circuits protected by them could still trip the upfront RCD as well.
The MCBs are single pole, so you are only really replacing like with like installing single pole 30 mA RCBOs, but adding 30 mA RCD additional protection.
The MCBs are single pole, so you are only really replacing like with like installing single pole 30 mA RCBOs, but adding 30 mA RCD additional protection.
I want to replace the 2 light circuits mcbs ( both 6amp) + 1 socket circuit mcb ( 20amp no outside equipment) with RCBO protection but due to size, I can only fit the single pole type. The date on this board is 2000.
Thanks but would that comply with the latest regs?.
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Coloumb
Screwfix Select
If you want to comply with the latest regs realistically you would need to fir an 18th edition CU, ie metal. Are you wanting to rent the property?
Thanks for your reply, I don't want to rent my house I just want it to comply with the electrical safety criteria.
Sorry got a bit confused there, I am informed that the current setup would be a C2 safety issue, therefore these circuits need to be 30ma RCBO protected, The Schneider (who took over Square D) installation instructions state that their SP RCBOs are not suitable for TT systems?
Yes it would. Single pole RCBOs are perfectly acceptable on a TT supply if you have an up-front RCD, which should be time delayed to provide some discrimination.
The Happy Builder
Screwfix Select
It’s all about isolation and switching for mechanical maintenance.
Single pole devices such as MCBs, RCBOs and AFDDs can be used as an isolator whilst working on a circuit in a TN earthed installation, because the neutral is considered to be at zero volts.
But in a TT earthed installation there will be a voltage present on the neutral, so both live and neutral conductors need to be isolated to work on a circuit, so the main switch has to break all the conductors and be used as the isolator unless there is another suitable isolator in the circuit.
In your installation the main switch should be used to isolated the downstream devices which are protected by single pole circuit protective devices, not those single pole devices.
https://electrical.theiet.org/wirin...ion-and-switching-for-mechanical-maintenance/
To add to that in single phase domestic installations the main switch has to break the neutral, but it doesn’t have to in three phase domestic installations or both single and three phase non-domestic installations for the same reasons.
Single pole devices such as MCBs, RCBOs and AFDDs can be used as an isolator whilst working on a circuit in a TN earthed installation, because the neutral is considered to be at zero volts.
But in a TT earthed installation there will be a voltage present on the neutral, so both live and neutral conductors need to be isolated to work on a circuit, so the main switch has to break all the conductors and be used as the isolator unless there is another suitable isolator in the circuit.
In your installation the main switch should be used to isolated the downstream devices which are protected by single pole circuit protective devices, not those single pole devices.
https://electrical.theiet.org/wirin...ion-and-switching-for-mechanical-maintenance/
To add to that in single phase domestic installations the main switch has to break the neutral, but it doesn’t have to in three phase domestic installations or both single and three phase non-domestic installations for the same reasons.
The Happy Builder
Screwfix Select
If that is TT earthed it’s completely noncompliant, unless the 100 mA S-type RCD is installed separately upfront in the meter tails.
If there is an additional upfront RCD in the tails then those single pole MCBs can be swapped for single pole RCBOs, but none of the single pole devices should be used as isolators, if any work is being done only the double pole upfront RCD, main switch RCBOs or 30 mA RCD can be used to provide safe isolation.
If there is an additional upfront RCD in the tails then those single pole MCBs can be swapped for single pole RCBOs, but none of the single pole devices should be used as isolators, if any work is being done only the double pole upfront RCD, main switch RCBOs or 30 mA RCD can be used to provide safe isolation.
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It is installed see last photo.
Great info thanks.