Search the forum,

Discuss MCCB with RCD settings in the UK Electrical Forum area at ElectriciansForums.net

Reaction score
51
MCCB with RCD bolt on, anyone know how to work these settings out? Ignore settings now but this is upfront RCD TT system so I want to top one to be 0.3 for 300mA but unsure on bottom?

4A051DE4-A81E-4B35-991F-3E4D76F0AB6F.jpeg


016B9063-754D-4364-9371-214F7D6C5946.jpeg
 
I not sure I understand the question. You do realise that the time setting on the device is marked in seconds, and so you need to convert milliseconds to seconds?
 
As a matter of interest, why does it need to be changed?
It was left on 0.1 so 100mA and was nuisance tripping, hench I’ve changed to 300mA
Is the question, what is the appropriate time delay setting for the installation?

The minimum that doesn't cause a nuisance and at or below the reg requirement or customers spec.
Yes that was all, couldn’t find anything online I knew how to set current just the time
 
So does that acheive disconnection times satisfactorily now that you have changed it to 3 x the original ma? Is it not the case if it is tripping that some investigation may be due? Maybe IR tests if it is possible?
 
That is commonly called a vigi module. You will notice when set for 30ma there is a line down indicating to set to no delay so additional rcd protection is provided.
 
So does that acheive disconnection times satisfactorily now that you have changed it to 3 x the original ma? Is it not the case if it is tripping that some investigation may be due? Maybe IR tests if it is possible?
Yes all sub circuits and feed from mains all tested fine with IR, now set to 300mA it’s all fine there’s discrimaination now 300mA to 100mA and so on, just didn’t understand the bottom dial
 
So does that acheive disconnection times satisfactorily now that you have changed it to 3 x the original ma? Is it not the case if it is tripping that some investigation may be due? Maybe IR tests if it is possible?
Yes all sub circuits and feed from mains all tested fine with IR, now set to 300mA it’s all fine there’s discrimaination now 300mA to 100mA and so on, just didn’t understand the bottom dial
 
It's a wind up this one. Guaranteed
It’s the bottom dial I can’t understand? So it just works on disconnection time but in milliseconds? So say I have no greater than 32A final circuits on TT which is 0.2 seconds then what do I set it?
No ---- take, spark I work with doesn’t know either and he’s just guesses where as I’d like to know how and why it’s set like that
 
But you were asking what delay a TT circuit should be set to. Are you saying you know this, but need to convert seconds to milliseconds?

To answer that, there are 1000mS in a Second.
 
It is a variable earth leakage modual that is used with a mccb eather bolted on or using a shunt trip module

The top part is to set trip current
Bottom is to set a time delay

They are mainly used on sub circuits or large motors ect were the time delay can offer some sort of discrimination

Remember earth leakage is cumulative
 
But you were asking what delay a TT circuit should be set to. Are you saying you know this, but need to convert seconds to milliseconds?

To answer that, there are 1000mS in a Second.
Ok so it’s TT, in this panel you have Main MCCB/RCD one in picture then 3 X BS88 fuses which feed some electric boxes with 16A sockets with relevant 30mA RCBOs
 
I'm still confused. Do you not know what the regs require, or do you not get the seconds/milliseconds thing?
 
It is a variable earth leakage modual that is used with a mccb eather bolted on or using a shunt trip module

The top part is to set trip current
Bottom is to set a time delay

They are mainly used on sub circuits or large motors ect were the time delay can offer some sort of discrimination

Remember earth leakage is cumulative
Thanks is there a way to understand how to set the time delay?
 
It is a variable earth leakage modual that is used with a mccb eather bolted on or using a shunt trip module

The top part is to set trip current
Bottom is to set a time delay

They are mainly used on sub circuits or large motors ect were the time delay can offer some sort of discrimination

Remember earth leakage is cumulative
Thanks is there a way to understand how to set the time delay?
 
First you need to know what function it is required for. Secondly you need to consider upstream devices and how they are operating then the vigi module can be set to ensure coordination is achieved.
 
The RCD protection for the final circuits running to the sockets is this RCD unit.
The maximum time allowed for disconnection of a final circuit, rated 63A or less, containing socket outlets, on a TT system, is 0.2s.
The sockets themselves have local 30mA RCD protection.
You need to ensure that if there is a fault on a socket that the local 30mA RCD trips before the main RCD unit you pictured, to avoid disconnecting other circuits unnecessarily.
The 30mA RCDs will have no pre set time delay so they must disconnect within 40ms (0.04s) when there is a significant fault current (in testing terms when the current is 5*Iδn). (or 300ms at Iδn)
Therefore in order to provide at least partial discrimination to ensure the individual sockets disconnect first you have to set the time delay for the RCD unit to above 0.04s and below 0.2s.
To ensure, according to the maximum limits in the regulations, that each socket always went first you would have to set the time delay above 0.3s but this would not be allowed by the maximum disconnection time limit of 0.2s. Most RCDs would practically disconnect far faster than 300ms at Iδn so discrimination would be achieved in practice at values lower than 300ms, perhaps 100ms might be a good compromise?
 
If it’s a distribution circuit fed from the 300mA then disconnection time is 1 sec
Set it up then test for compliance with your red tester.
30mA rcd for sockets are correct for final circuits fo protection of persons or livestock.
300mA used as fire protection for earth fault on the distribution cable.
 
BS7671 appears to have dropped the requirement for 30mA RCDs to operate within 40ms.

The requirement is still there, according to BBB 643.8 and OSG 11.5

I think some confusion may have arisen due to the dropping of one of the columns on the test sheet. There is now only one column for trip time. If additional protection is required for a particular circuit, you would record the value measured at 5 X the rated operating current. Otherwise you would record the value measured at 1 X the rated operating current.
 

Reply to MCCB with RCD settings in the UK Electrical Forum area at ElectriciansForums.net

Similar Threads

We are looking for a distribution board to provide 3 * 160A three-phase feeds, but they are basically redundant supply path options so max total...
Replies
4
Views
336
I have an new set of circs here... Landlord in Cyprus EICR needed in empty flat. No credit on meter. Need power for Ze (TNCS) and RCD test at...
Replies
11
Views
504
Evening everyone… I’ve attached pictures for your leisure.. so basically the customer does not have any RCD protection.. 3036 fuseboard is in...
Replies
9
Views
437
Called out to fault on RCD tripping maybe twice in a month for sometime. Did all the tests & found RCD was faulty, Refitted a new Rcd Type A which...
Replies
2
Views
868
I was wondering what is the cheapest option to get a (legitimate) copy of the EN standards, such as IEC/EN 62305 on lightening protection? I...
Replies
13
Views
701

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

YOUR Unread Posts

This website was designed, optimised and is hosted by untold.media Operating under the name Untold Media since 2001.
Back
Top