Type B and C RCBO's together?

[timo1]

Hello,

After feeling pleased with myself for installing and testing a new CU ready for my NICEIC inspection, I noticed that one of the RCBO's I bought is a type B where the other circuits are type C, the circuits are:

Heating - 16A type B RCBO
Ring main - 32a type C RCBO
Cooker - 40A type C RCBO
I have another radial circuit which is a socket on a 16A type C RCBO as it is only used for a tumble dryer.

A pretty dumb oversight I know, my question is will I have to replace the type B to match? I read a thread which said most RCBO's are type C and acceptable for domestics and all the readings and tests are within regs, normally I would just buy another one but this inspection is costing a small fortune and if I can get away without changing it then that would be great.

 

[bugsy]

Are the earth loops low enough for type c

 

[timo1]

Hi,

The ring main is 0.50ohm max is 0.58 for a 32A.
cooker is 0.33 compared with a max of 0.46 for a 40A
other 16A radial is 0.26 max 1.16 (really short leg)

I have checked OSG page 103 Table 2d for above. Is this ok?

 

[bugsy]

Then you don't appear to have a problem

 

[timo1]

Thanks for the quick reply appreciate your time.

 

[telectrix]

looks OK to me. possible change just one C type to B type on the ring as the reading is close to the max.

 

[Mr Mark Sparks]

that is the 80% reading .72 is max for c32

 

[telectrix]

i stand corrected.

 

[sparkswillfly]

what earthing do you have tt tns tncs then have a look in the osg pages 44 -51 hope this help i would hate you to have a revisit

 

[jedisparks]

Also Zs is less of an issue when RCBOs or RCDs are protecting the circuit. so no probs

 

[pushrod]

If it is your place just say you put the C type in because you are thinking of upgrading the cooker to one with an induction hob and you know that you will need one then.
You might even score some brownie points for showing your knowledge and planning ahead

edit: didn't read your first post properly initially thought you had just put a C type on the cooker. Although you can get away with the C's the mcb's at least are recommended for general use in commercial and industrial installations. For the sake of the extra cash i would switch them to B's would be my feeling - you can always keep them for future use and it will save you answering awkward questions on your assessment.

 

[Mr Mark Sparks]

Also Zs is less of an issue when RCBOs or RCDs are protecting the circuit. so no probs

yes but the max zs to be recorded is that listed in the regs for 60898 and 61009 circuits should be designed to meet these

 

[jedisparks]

fair point! and for the purposes of an assesment it is best to not have anything for an assesor to flag up. In reality the RCBO or RCD will break well within the max disconnection time regardless of the Zs being a tad high.

 

[nickblake]

Also Zs is less of an issue when RCBOs or RCDs are protecting the circuit. so no probs

Correct but nice to get it within the permitted values

 

[jedisparks]

Yes always nice to be within permitted values

 

[Farmelectrics]

is the 80% value the one out the regs and the other out of osg seems daft to me having two different values what do they mean by the 80% value please explain

 

[pushrod]

is the 80% value the one out the regs and the other out of osg seems daft to me having two different values what do they mean by the 80% value please explain

BS7671 gives Zs values at their max operating temp so if you are taking the reading at a lower temp you would want a lower value.(Resistance increases as temp increases) It can be calculated accurately or you can use "the rule of thumb" approximation and take .8 of the value for readings at normal temp. The OSG in appendix 2 gives its readings as if the temp was 10 celcius and table 2E in the OSG gives correction factors for other temps.
The R1+R2 values in App 9A of the OSG are given for 20 celcius and table 9B gives correction values for other temps - you do get used to it in time