Max Zs - 16 amp Type D mcb

[sparks2911]

he guys - a little help needed if you dont mind..... what is the maximum permissable Zs for a 16 amp type D mcb. I got a customer whose B type keeps tripping every time he powers up his compressor.

thanks in advance

 

[Bez]

0.58, Corrected

 

[Revved Up Sparky]

he guys - a little help needed if you dont mind..... what is the maximum permissable Zs for a 16 amp type D mcb. I got a customer whose B type keeps tripping every time he powers up his compressor.thanks in advance

0.57 ohms (on the chart on the inside page of my book of NICEIC Minor Works Certificates)

....but in table 2D/ page 103 of the OSG it is indeed 0.58 ohms.

 

[sparks2911]

cheers for that Bez - so 0.49 Zs at furthest outlet is just within.

 

[Bez]

cheers for that Bez - so 0.49 Zs at furthest outlet is just within.

I reckon so, as I say that figure is corrected so actual Max Zs will be higher than 0.58.

 

[batty]

Why not use a c type?

?:|

 

[sparks2911]

hi batty - to be honest did contemplate using C type but customer is a tight wad andwont fancy paying for mcb twice if the C type dont hold. Figure its just easier to for a D type

 

[Evans Electric]

A type C should be OK for a compressor , Sparks.

 

[batty]

B= domestic.

c= motor rated also fluorescent banks etc with high start up currents.

d= welders, xray machines etc with really high inrush currents.

c type should be ok for compressors.

 

[Lurch]

c type should be ok for compressors.

And so should a D. As long as the circuit is within specs either would be fine.

 

[netblindpaul]

Unless Zs is out, fit a D type and be done with it!

No comebacks, circuit complies, minimal risk of nuisance tripping.

I have seen many motor circuits trip C types, depending on the mechanics of the load, etc. and compressors can be a pain, especially if they try to start on full load, which they can, depending on the pneumatics side.

 

[netblindpaul]

Just realised at #4 the OP references outlets, this inferrs a ring or radial circuit with s.o.

I guess 13A type.

If the compressor is on its own dedicated circuit which unless domestic it really should be, minmise inconvenience in the event of a fault, and a host of others...

IF it is pugged into a ring, then other "base" loads will have an effect on the breaker tripping, and, a C or D type may not be appropriate, it should be carefully considered.

Also, if not on a dedicated radial, the FFS! A 1 pole D16 is a tenner list! IF it is on a dedicated radial, then the original design was insufficient to allow for the inrush. Still D16 3pole around

 

[seajayess]

You can work out Zs for MCB if you dont have any referance books.

B=5x current

C=10x current

D=20x current

so 16 Amp Type D = 16x20=320 Amps

230 Volts/320 Amps=0.718 ohms

correctoin factor = 0.8

0.718 x 0.8 = 0.574

so Zs = 0.574 rounded up to 0.58

Hope this helps CJS