Eicr ring main readings

[cliffed]

Would you guys be happy with these readings on ring main,Rcbo c type 30ma/32 amp.
r1 1.87...rn 1.91 cpc 3.20....R1 +R2.1.26.
zs 1.46 ohms.

 

[telectrix]

some long ring you have there.
[automerge]1573984432[/automerge]
r!+r2 = 5.07 ohms. this equates to approx. 250m, or there's something wrong.

 

[cliffed]

Yea,would it comply,Max allowed 0.68 ohms,but......

 

[sinewove]

some long ring you have there.

Sounds like roughly 270m of cable there thought max was about 100m of 2.5mm.S

 

[Ian1981]

As long as there is no volt drop concerns for the circuit and the rcbo when tested gives adequate earth fault protection, then it is what it is.

 

[Andy78]

Is it actually that long ? Those would be the highest readings I've ever seen for such a circuit.

 

[Ian1981]

Works out at 258 meters from the R1+R2 result assuming 2.5mm T&E

 

[Baddegg]

What size cable is it?....and why a “c” type?....I have no answer to your question but am genuinely interested ?

 

[cliffed]

2.5 mm lsoh t&e,measurement correct,it’s along one,also did short circuit measurement,according to my cals it does not comply.

 

[cliffed]

Is it actually that long ? Those would be the highest readings I've ever seen for such a circuit.

scary ain’t it.

 

[SJD]

It is quite a long circuit, but from the fact that it is a C32 RCBO, I'm suspecting this is commercial / industrial, rather than domestic? For example, a ring in a large workshop, warehouse, school, etc.

I'd be wondering about the voltage drop, e.g. are all the loads at middle of the ring because the outlets happen to be a long way from the distribution board?

Or has someone used a somewhat too small cable size, e.g. 1.5mm2 T&E or SWA?

 

[cliffed]

It’s in a quite a large office area,it’s defo 2.5mm,difficult to judge where the actual loads are,there are mainly,computers plugged in.Been in service @ least 5 years,all signed of.

 

[Baddegg]

It’s in a quite a large office area,it’s defo 2.5mm,difficult to judge where the actual loads are,there are mainly,computers plugged in.Been in service @ least 5 years,all signed of.

That sounds like most of my customers.....worked fine like that for years ?

 

[telectrix]

It’s in a quite a large office area,it’s defo 2.5mm,difficult to judge where the actual loads are,there are mainly,computers plugged in.Been in service @ least 5 years,all signed of.

if that's the case, why not replace MCB with a B type, even drop to a 20A?

 

[cliffed]

T9

if that's the case, why not replace MCB with a B type, even drop to a 20A?

true that could be done,note on recommendations.
Even rcbo @ 20 amp

 

[Gary latto]

Sorry to hijack the post but for someone still learning how do you work out the length of circuit from the readings ie what would the formula be please ? Tia

 

[Julie.]

Sorry to hijack the post but for someone still learning how do you work out the length of circuit from the readings ie what would the formula be please ? Tia

Look in the on-site guide, appendix, I think it's table 11

It gives the R1+R2 resistance per metre

So for 2.5/1.5 it's around 19.5 miliohm per metre if you know the length, it's length x this value, if you know the overall resistance it's the resistance devided by the resistance per metre

You could also work it out from R1 for 2.5mm2 per metre, plus R2 for 1.5mm2 per metre

These values are also in the table

 

[Gary latto]

Thanks Julie appreciated ?

 

[Pretty Mouth]

For a ring final, use an end-to-end reading, eg. the line conductor r1.

Length of conductor = resistance of conductor ÷ resistance of conductor per meter

For a 2.5mm² conductor, resistance per meter is 7.41mΩ, or 0.00741Ω. So:

Length of conductor = r1 ÷ 0.00741

 

[Gary latto]

Cheers pretty mouth ?