Garage Consumer Units

[Jonny72]

Are you going to incorporate surge protection into it?

Prob not. It's my own garage. Washing machine, dryer etc, lights etc. But yea know were you coming from prob fact I don't fit one will regret it later Murphy's Law. Actually was looking to see if maybe room in the main consumer. Unit for Type 2 but there is not. If I was getting on I would prefer to protect whole house. Maybe see if it can be done as stand alone enclosure at main consumer unit.. Cheers Jonny

 

[pc1966]

You will need RCD protection somewhere is virtually every case. If it is fed via SWA cable so no need for protection on the distribution cable then it makes sense to have just a MCB at the house CU and then RCD and any other MCBs at the garage.

However, if you can't be sure of the sub-main installation then having RCD/RCBO at house and then just MCB at the garage is a better choice.

Two 30mA RCD in series without selectivity is poor design, not enough to worry about on an EICR beyond C3, but not something you should aim to do unless you have a very good reason.

Having said that, having MCB in series or RCBO+MCB will have negligible fault selectivity, even if they are OK on overload due to a 1.6:1 or greater difference in rated current. Again, not good design, but usually an acceptable trade-off if the final circuits in the garage are not critical as done in practically every case.

 

[westward10]

You can only neglect RCD protection if ADS is provided without it.

 

[pc1966]

You can only neglect RCD protection if ADS is provided without it.

Indeed, making the typical TN assumption here that end of distribution Zs is low enough for MCB disconnection in under 5s.

 

[Dustydazzler]

Indeed, making the typical TN assumption here that end of distribution Zs is low enough for MCB disconnection in under 5s.

For us domestic sparks anything under 1 ohm Zs would be acceptable for ADS for 99% situations

 

[Jonny72]

You will need RCD protection somewhere is virtually every case. If it is fed via SWA cable so no need for protection on the distribution cable then it makes sense to have just a MCB at the house CU and then RCD and any other MCBs at the garage.

However, if you can't be sure of the sub-main installation then having RCD/RCBO at house and then just MCB at the garage is a better choice.

Two 30mA RCD in series without selectivity is poor design, not enough to worry about on an EICR beyond C3, but not something you should aim to do unless you have a very good reason.

Having said that, having MCB in series or RCBO+MCB will have negligible fault selectivity, even if they are OK on overload due to a 1.6:1 or greater difference in rated current. Again, not good design, but usually an acceptable trade-off if the final circuits in the garage are not critical as done in practically every case.

Thanks great advice and that's my plan. So MCBs in parallel not a good idea either?? That warrant a C3? Don't want to design code breaking into the circuit. Cheers Jonny

 

[westward10]

You have an HNC in electrical engineering so the design of this should be straight forward.

 

[Jonny72]

You have an HNC in electrical engineering so the design of this should be straight forward.

I was used wiring and designing high end avionic equipment and power supply in trainee fighter aircraft a past life so slightly different area of expertise. I do have an NVQ3. I come on here to get advice as I know I don't know everything. Before anyone says leave it to professionals - And I am updating my skill base having completed C&G 18th Edition and CG Initial Verification and Periodic Testing. I do concede I get stuck and use this forum to bounce ideas with the helpful people on here of which there are plenty. Thanks Jonny.

 

[Jonny72]

Indeed, making the typical TN assumption here that end of distribution Zs is low enough for MCB disconnection in under 5s.

No doubt will be, TNCS and last Ze was 0.22 ohms.

 

[Jonny72]

You will need RCD protection somewhere is virtually every case. If it is fed via SWA cable so no need for protection on the distribution cable then it makes sense to have just a MCB at the house CU and then RCD and any other MCBs at the garage.

However, if you can't be sure of the sub-main installation then having RCD/RCBO at house and then just MCB at the garage is a better choice.

Two 30mA RCD in series without selectivity is poor design, not enough to worry about on an EICR beyond C3, but not something you should aim to do unless you have a very good reason.

Having said that, having MCB in series or RCBO+MCB will have negligible fault selectivity, even if they are OK on overload due to a 1.6:1 or greater difference in rated current. Again, not good design, but usually an acceptable trade-off if the final circuits in the garage are not critical as done in practically every case.

And thankyou that was great advice. J