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I need a Type C MCB at the fuse box for my compressor.
Existing is a Dorman Smith LLR 32T3

I read on an ebay advert, that Type 3 was the Old Type C. I cannot find anything to support that.

Please could you advise if Type 3 has replaced Type C?

thank you

glassescase

Not qualified to advise but thought your question worth googling and found this:

B types - 3 to 5x In
C types - 5 to 10x In
D types - 10 to 20x In
where as the old types:
type 1 - 2.7 to 4x In
type 2 - 4 to 7x In
type 3 - 7 to 10x In

So looks like 'yes'.

thank you arco_iris
I took the chance and started the compressor, did not trip the "fuse". Now wondering if 32amp is too big, maximum start up current is 30 amp and running amperage is 20.
Off to recheck paper work

thanks again

glassescase

glassescase wrote: ↑Sun Mar 20, 2022 2:27 pm thank you arco_iris
I took the chance and started the compressor, did not trip the "fuse". Now wondering if 32amp is too big, maximum start up current is 30 amp and running amperage is 20.
Off to recheck paper work

thanks again

glassescase

The circuit breaker is to protect the cable, not the appliance. What size is the cable AND be aware that unless you verify the Zs use of a type 3 or C type isn’t a great idea

Neelix wrote: ↑Sun Mar 20, 2022 5:43 pm

glassescase wrote: ↑Sun Mar 20, 2022 2:27 pm thank you arco_iris
I took the chance and started the compressor, did not trip the "fuse". Now wondering if 32amp is too big, maximum start up current is 30 amp and running amperage is 20.
Off to recheck paper work

thanks again

glassescase

The circuit breaker is to protect the cable, not the appliance. What size is the cable AND be aware that unless you verify the Zs use of a type 3 or C type isn’t a great idea

Type C is in the instructions. what is Zs? 6mm cable should do

glassescase

glassescase, Zs is a measurement of sorts, Loop impedance and resistance. Not summat that the above average DIYer can measure. Just because electrics work doesn't mean it's safe.

wine~o wrote: ↑Sun Mar 20, 2022 7:08 pm glassescase, Zs is a measurement of sorts, Loop impedance and resistance. Not summat that the above average DIYer can measure. Just because electrics work doesn't mean it's safe.

The OSG gives maximum lengths for different cable sizes according to what size/type of MCB is used/type of supply to the house/RCD or no RCD protection.

OK so it's only a rule of thumb but could be used to help out the OP.

OnlyMe wrote: ↑Tue Mar 22, 2022 6:16 pm

wine~o wrote: ↑Sun Mar 20, 2022 7:08 pm glassescase, Zs is a measurement of sorts, Loop impedance and resistance. Not summat that the above average DIYer can measure. Just because electrics work doesn't mean it's safe.

The OSG gives maximum lengths for different cable sizes according to what size/type of MCB is used/type of supply to the house/RCD or no RCD protection.

OK so it's only a rule of thumb but could be used to help out the OP.

OSG?

Glassescase

glassescase wrote: ↑Tue Mar 22, 2022 6:59 pm

OnlyMe wrote: ↑Tue Mar 22, 2022 6:16 pm

wine~o wrote: ↑Sun Mar 20, 2022 7:08 pm glassescase, Zs is a measurement of sorts, Loop impedance and resistance. Not summat that the above average DIYer can measure. Just because electrics work doesn't mean it's safe.

The OSG gives maximum lengths for different cable sizes according to what size/type of MCB is used/type of supply to the house/RCD or no RCD protection.

OK so it's only a rule of thumb but could be used to help out the OP.

OSG?

Glassescase

OSG = BS 7671 On Site Guide - used by sparks

Neelix wrote: ↑Tue Mar 22, 2022 7:01 pm
OSG = BS 7671 On Site Guide - used by sparks

And it does list some scenarios where the OP may be OK with a 32A C type MCB. And some where it's not

OnlyMe wrote: ↑Tue Mar 22, 2022 7:07 pm

Neelix wrote: ↑Tue Mar 22, 2022 7:01 pm
OSG = BS 7671 On Site Guide - used by sparks

And it does list some scenarios where the OP may be OK with a 32A C type MCB. And some where it's not

what are the not ones? I dont have a copy but a sparks did my wiring at the other house and used a type c.

Glassescase

You need to know what type of supply you have to the house. If you do not know what that means it's probably easier to post a photo of your electrical cut out/main incoming fuse etc and I am sure we can tell you. Or a sticker saying PME connection on the main fuse holder usually gives the game away:-)

The worst case is a TN-S supply with no RCD. Any idea of the length of cable from the CU to the compressor? Is it direct from the main CU or from from a garage CU? These questions and their answers do make a difference.

OnlyMe wrote: ↑Tue Mar 22, 2022 7:07 pm

Neelix wrote: ↑Tue Mar 22, 2022 7:01 pm
OSG = BS 7671 On Site Guide - used by sparks

And it does list some scenarios where the OP may be OK with a 32A C type MCB. And some where it's not

That rather depends on the Ze

The magnetic part of a MCB/RCBO works in around 0.01 seconds, where the thermal part can take far longer to work, so to ensure the magnetic part can work the prospective short circuit current (PSCC) needs to be high enough, ohms law means we can express it as either PSCC or in impedance, so type C will trip at 10 times rated thermal trip current using magnetic part, we allow for a 5% volt drop, so working on 218.5 volt, so 218.5/320 = 0.68Ω and the DNO supply is normally around 0.35Ω so 0.33Ω for internal wiring, so a 6 mm² cable is around 0.0073Ω per meter, so around a 45 meter limit for the cable, with 4 mm² then 0.011Ω so 30 meter maximum.

Since the Tabulated mV/A/m is affected by temperature there is a Correction factor Ct so not exactly to those figures, but near enough.

This is what it being refereed to when talking about Ze.

OnlyMe wrote: ↑Tue Mar 22, 2022 7:36 pm You need to know what type of supply you have to the house. If you do not know what that means it's probably easier to post a photo of your electrical cut out/main incoming fuse etc and I am sure we can tell you. Or a sticker saying PME connection on the main fuse holder usually gives the game away:-)

The worst case is a TN-S supply with no RCD. Any idea of the length of cable from the CU to the compressor? Is it direct from the main CU or from from a garage CU? These questions and their answers do make a difference.

compressor is served from the consumer unit in the garage, a bit over 10 meters may be around 15 meters. The house consumer unit has a 40 amp cct breaker serving the garage. The incoming main goes to a "grey box" that has series 7, type 2b and BS1361 stamped on it. I say 2b, it is roman numerals like a capitol i but I cant type a proper capitol i. From there to a meter and from the meter to a fuse? The consumer unit in the garage did have a fuse location already marked up as compressor. Could not see a sticker.

glassescase