RCBO test Results

[Gadget123uk]

Hello Guys,

Can you help with a problem we had today.

We have installed a ring circuit of exterior 70 watt MHi floodlights around the perimeter wall of a building. There are 16 lights on a ring of fire tough 2.5 R1 + RN with 1.5 R2.
The cable length is 230 meters. The ZS = 0.71. R1 = 1.59. RN = 1.59. R2 = 0.95.
We installed a 16 amp 10K RCBO but the reading we got on RCD test were X1 550/550 X5 440/ 440.
Both reading outside of Bs7671.
These reading were obtained with a raw circuit, straight out of the RCBO into the ring.
Does anyone have an idea why the readings were so high so as not to comply?
We have as a temporary measure (we hope) installed a MCB with no problems.
Regards
Gadget.

 

[Richard Burns]

Were the lights connected whilst you were testing as they may have been "balancing" the differing load and delaying tripping.
An RCD test should ideally be done with no loads on the RCD and tested at the RCD terminals.
Try testing the RCBO without any circuit attached.

 

[MarkieSparkie]

This appears to have been posted in the wrong section of the forum, when tidying up could a moderator move it an appropriate place.

 

[Geoffsd]

The ZS = 0.71. R1 = 1.59. RN = 1.59. R2 = 0.95.

That can't be right.

 

[telectrix]

could be with frire tuff. the foil is in contact with the cpc thus increasing the effective csa.

 

[Gadget123uk]

Hello,

Thats an interesting theory, will look into on next visit to site.

Many thanks

 

[Gadget123uk]

The figures quoted are what we got.

Strange yes but the only way for us to go from here is to.
1) Disconnect all the light fittings and retake measurements.
2) Also carry out test on foil of fire tough to see if any contact with CPC
to alter the prospective results.
Many thanks guys.

 

[Richard Burns]

The figures quoted are what we got.

Strange yes but the only way for us to go from here is to.
1) Disconnect all the light fittings and retake measurements.
2) Also carry out test on foil of fire tough to see if any contact with CPC
to alter the prospective results.
Many thanks guys.

You will not need to disconnect all the fittings simply switch off, or remove the cables from, the MCBs in the board (when it is off!) so that no load is connected to the RCD once you start testing.

The foil of the cable should be in contact with the CPC as this is the design of the cable; the effect of this is to have a large cross sectional area cpc which will have a lower resistance than the line and neutral conductors (i.e. for your ened to end values 0.95 is less than 1.59)

 

[1shortcircuit]

The foil of the cable should be in contact with the CPC as this is the design of the cable; the effect of this is to have a large cross sectional area cpc which will have a lower resistance than the line and neutral conductors (i.e. for your ened to end values 0.95 is less than 1.59)

I've not used this type of cable before so it's nice to learn this. Thank you :thumbsup