High Integrity Earthing

[Electro-tech]

Hi Guy's, Need your take on a commercial office IT environment. I am getting earth leakage total of 26mA, okay, spread over 22 workstations & 4 Server & ups IT devices, not bad. The power RFCircuits are fortunately spread over a split load board / 2 RCD's. No nuisance tripping reported. Subject to 543.7.1.3.203 High integrity earth connections is necessary etc. I have yet to remove a Socket to inspect as I need to shut down their servers on this weekend. I do know that at the DB the circuits are 2.5mm T&E so cpc is undersized. Just to confirm on a EICR how would you code it, & any further comments welcome. Thanks, guys in advance.

 

[Pete999]

Hi Guy's, Need your take on a commercial office IT environment. I am getting earth leakage total of 26mA, okay, spread over 22 workstations & 4 Server & ups IT devices, not bad. The power RFCircuits are fortunately spread over a split load board / 2 RCD's. No nuisance tripping reported. Subject to 543.7.1.3.203 High integrity earth connections is necessary etc. I have yet to remove a Socket to inspect as I need to shut down their servers on this weekend. I do know that at the DB the circuits are 2.5mm T&E so cpc is undersized. Just to confirm on a EICR how would you code it, & any further comments welcome. Thanks, guys in advance.

I would code the situation as "needing further investigation" If you feel there is a danger, then time should be arranged for a system power down to enable this "further investigation", the client needs to be made aware of the possible consequences of leaving the installation in it's current state, should there be a problem.

 

[Nigel]

If you can confirm the CPC size then FI is not appropriate IMO. I would say a C3 so long as there is no nuisance tripping.

 

[Pete999]

If you can confirm the CPC size then FI is not appropriate IMO. I would say a C3 so long as there is no nuisance tripping.

The OP has stated in his opening post that he has a measured Earth Leakage of 26 mA regulation 543.7.2.201 clearly states that Final circuits feeding socket outlets or connection units, where the pcc in normal service is likely to exceed 10mA then they require a high integrity cpc, the cpc of a Radial circuit should be in the form of a ring, and if the circuit is in metallic conduit or metallic trunking an extra cpc should be installed.
Diagrams depicting this can be found in the 18th edition OSG Page 87, the I have to disagree with essex ensuring the size of the cpc is not sufficient in my book.

 

[Deleted member 26818]

One of the problems here is the OSG and BS7671 contradict themselves.
BS7671 requires there be two CPCs.
The OSG just one CPC, terminated at different terminals at each accessory.

 

[westward10]

From what I can see this leakage is a combined sum over several final circuits thus each final circuit may be less than 10ma.

 

[Pete999]

From what I can see this leakage is a combined sum over several final circuits thus each final circuit may be less than 10ma.

Could well be Westward, suggest the Op could clarify this issue?

 

[Pete999]

Hi Guy's, Need your take on a commercial office IT environment. I am getting earth leakage total of 26mA, okay, spread over 22 workstations & 4 Server & ups IT devices, not bad. The power RFCircuits are fortunately spread over a split load board / 2 RCD's. No nuisance tripping reported. Subject to 543.7.1.3.203 High integrity earth connections is necessary etc. I have yet to remove a Socket to inspect as I need to shut down their servers on this weekend. I do know that at the DB the circuits are 2.5mm T&E so cpc is undersized. Just to confirm on a EICR how would you code it, & any further comments welcome. Thanks, guys in advance.

Just to clarify something Westeard10 mentioned, can you clarify how many circuits you are talking about, in essence if its more than one circuit what is the max EL measured per circuit, or is it just 1 circuit, in hindsight should have asked these question before I went chapter and verse, good point Westward though.

 

[Devonchris]

Would it be possible to split the 2 rfc's into 4 radials on their own RCBO thereby removing the need for high integrity earth? If there are no spare ways then a new extra board would be easier than practically rewiring the place.

I suppose it depends on wether the leakage is distributed evenly across the circuits but it may remove the need for all the circuits to have a high integrity earth.

 

[Deleted member 26818]

Could split into Radials with the CPC left as a ring.

 

[I Dunno]

By splitting the ring into radials you would be at risk of having higher leakage so no. Could keep cpc as ring, but in reality, the best way to go would be 4mm seperate clean earth throughout.
The price to install is surely justifiable to avoid future nuisance tripping.

 

[Deleted member 26818]

Not sure how splitting the ring would result in higher leakage?
Also, not aware there has been any nuisance tripping?

 

[Nigel]

The OP has stated in his opening post that he has a measured Earth Leakage of 26 mA regulation 543.7.2.201 clearly states that Final circuits feeding socket outlets or connection units, where the pcc in normal service is likely to exceed 10mA then they require a high integrity cpc, the cpc of a Radial circuit should be in the form of a ring, and if the circuit is in metallic conduit or metallic trunking an extra cpc should be installed.
Diagrams depicting this can be found in the 18th edition OSG Page 87, the I have to disagree with essex ensuring the size of the cpc is not sufficient in my book.

My point was FI is not appropriate as the op knows all the details. Would you code it differently to a C3?

 

[westward10]

We need to know how this leakage has been measured, combined across all final circuits?

 

[Pete999]

We need to know how this leakage has been measured, combined across all final circuits?

Agree should have asked that question at start off.

 

[Wilko]

Hi - sorry if you've already seen it @Electro-tech, but for the socket outlets on RFC check out 543.7.2.201 and part (i) particularly. This means outlets need re-terminating etc rather than new cpc needing to be run in. Tin Hat on.

 

[Electro-tech]

We need to know how this leakage has been measured, combined across all final circuits?

Hi Guys, Thanks for the replies. The measured Earth leakage was a combined reading with a Megger DCM300E Earth Leakage Clamp meter on the 16mm cable from MET in the DB. I could not test each circuit as I need to power down to open up the DB out of hours at the weekend. Can't risk knockin a RCD test button while in use.I honestly think that the installation Earth integrity was not designed for IT office use in the first place. I would like to see a 4mm cpc installed .You can tell that the installation overall was not installed correctly going by the T& E runs stuffed in plastic conduit . Main runs are T&E in metal trunking,why not singles. I will measure each circuits leakage separately at the weekend & report back.

 

[Electro-tech]

Hi - sorry if you've already seen it @Electro-tech, but for the socket outlets on RFC check out 543.7.2.201 and part (i) particularly. This means outlets need re-terminating etc rather than new cpc needing to be run in. Tin Hat on.

Okay Wilko noted, but if you have dado trunking while re-terminating the outlets I would like to run the 4mm. The only thing that I do not know at the moment is, are there 1 or 2 earth terminals on the existing accessories?

 

[westward10]

You definitely need to assess each final circuit before deciding on any works as they may not be required.