C type / D type - differences and advise

[Blackstone]

Afternoon all,

What are the differences in C and D types breakers (MCB's)?

What type would you say should be fitted to a refrigeration unit with compressor, lights, fans and a 800w drip tray heater?

We have some conflicting views in the office with some saying C type breakers should be fitted and some saying D type should be fitted

Let me know if you need more info

Cheers

Blackstone

 

[telectrix]

generally a C type will do. the difference between C and D is the magnitude of the surge current they will withstand without tripping. manufacturers instructions should be followed as regards the size and type of breaker to be fitted.

edit

: just seen that you are in kent, so a rusty nail is more commonplace> :drunk:

 

[D Skelton]

What are the differences in C and D types breakers

C types trip at roughly 10 times the rated current and D types trip at roughly 20 times the rated current.

Selection is based upon the start up (surge) current the equipment draws.

 

[loop3]

The physical difference is in the internal mechanism. As mentioned above, they're employed to overcome an initial surge. A time delay if you like. I was taught d type is used for xray or wielding equipment. C for motors and banks of fluorescent lights. Bear in mind not all manufacturers make d breakers for their boards.

 

[Blackstone]

: just seen that you are in kent, so a rusty nail is more commonplace> :drunk:

We ran out of rusty nails!

anyway...

The unit runs on a 16amp breaker and on initial start up of the compressor it can spike to 40-50amps


Is there any recommendations or guidance the says compressors should have a certain type of breaker (one comments from a old school ex-electrician)?
The old school ex-electrician also said that D types should only be used in industrial applications?

Just throwing those comments out there.....

 

[Silly Sausage]

This might help a little...

 

[telectrix]

my common sense tells me to fit a C type, and then if there's a problem with tripping on start up, consider uprating to a D type. obviously, the qucker the MCB trips in the event of a fault, the better. also consider the lower max. Zs value required for a D type.

 

[Guest55]

..... also consider the lower max. Zs value required for a D type.

This ^^^ will ultimately decide which you can use.

 

[Darkwood]

Its all down to the motor and manufacturers guide, you need to attain the recommended mcb from the manufacturer failure to source this info you can chack the motor rating and discuss with the mcb manufacturers, the college taught guide for B, C and D types is a crude rule of thumb thats generally ok to use in domestic, once you have established the mcb rating required then you design your circuit to suit the mcb rating this way you will be given different mcb types and rating and you can choose which one would satisfy permitted loop values.

This sometimes see you fitting a larger cable than you would have worked out if you did the standard teaching methods, and if your ZS values are of concern its possible to have a type B on larger circuit.

 

[johnboy6083]

I would find out the starting current & FLC of the motor. Then you can use that to select your MCB rating and type. Does the motor go through a Manual Motor starter type overload?

 

[Blackstone]

Zs values??

Feel like a right noob asking that!

 

[Darkwood]

Chapter 41 table 41.3 (BS 60898 / 61009-1)

Or the relevent table to your protective device.

These are you permitted Zs values ....

example;
32a (b) =1.44
32a (c) =0.72
32a (d) =0.32

You can see by changing the device to the next type you half the permitted Zs value so simple wiring the the circuit with a 32amp (b) then if it trips change it to a 'c' or 'd' isn't how you should plan things because one day it will catch you out and require a larger MCB rating and circuit design.
Ive given values direct from the reg's here but you should be aware of the 0.8 rule and if i recall the OSG takes this into account in printed values.

I hope i was just reminded you there Blackstone and not educating you

 

[Blackstone]

Ok

So if the start up current peaks at around 50amps, a 16amp C type breaker would be adequate.

I will obviously check with Compressor suppliers to confirm.

Assuming that right? thanks for all the helps guys.
Much appreciated!!