RCD RATING VS. SERVICE FUSE RATING

[spud1]

Hi chaps

A Wholesaler told me me this week that the RCDs in the new '18th' split load boards have to be rated at 100a because the 100a service fuse is only means of upstream overcurrent protection. But I was once told that service fuses, although marked as 100A on the cutout label are actually only actually 80amp?

Any thoughts guys?

 

[Nigel]

So for example (bear with me here as I'm not sure I have grasped this nonsense fully), In a single phase domestic situation the DNO fuse is 100A, CU main switch is 100A. A dual RCD load board is installed with 80A RCCBs. One would have to keep the total rating of all downstream devices for each RCCB less than 80A unless the manufacturer agrees that diversity can be used for that group of circuits ? But the total for the CU could be up to 160A as the main switch is in theory protected from overload ?

Spot on - although all UK manufacturers have said, through BEAMA that they will not permit diversity so the 95% of the regulation is void and a pointless exercise. The IET should have consulted the manufacturers before writing the reg and then just wrote what the manufacturers state.

The other alternative would be to have 100A RCCBs installed with the 100A main switch.

 

[Ian1981]

Hager now are supplying their dual rcd boards with 2 x 100amp 30mA rccb’s which are now type A with or with out an SPD

 

[Andy78]

Spot on - although all UK manufacturers have said, through BEAMA that they will not permit diversity so the 95% of the regulation is void and a pointless exercise. The IET should have consulted the manufacturers before writing the reg and then just wrote what the manufacturers state.

The other alternative would be to have 100A RCCBs installed with the 100A main switch.

So the OP's wholesaler was wrong with their assertion that all RCCBs will need to be 100A rated.

My example is how I used to arrange all my dual RCD boards anyway, but not installed any for a while now.

 

[Ian1981]

You can always just stick to rcbo consumer units

 

[Deleted member 26818]

I tend to agree but the Reg does state manufacturers info must be adhered to and they say you cannot take into account diversity. Why the IET just never wrote the Reg to state this and keep it simple is beyond me.

In your case if the OCPD is 100A or less then what is installed downstream is irrelevant.

What is the Reg No of the one that states Manufacturer’s info must be adhered to?

 

[Nigel]

So the OP's wholesaler was wrong with their assertion that all RCCBs will need to be 100A rated.

My example is how I used to arrange all my dual RCD boards anyway, but not installed any for a while now.

You are correct. I suppose the supplier is saying that we should assume 100A unless proven otherwise.

 

[Nigel]

What is the Reg No of the one that states Manufacturer’s info must be adhered to?

536.4.202

 

[Deleted member 26818]

532.4.202

In the words of Elvis: No such number.

 

[Nigel]

In the words of Elvis: No such number.

Apologies - now edited.

 

[Deleted member 26818]

That’s in relation to a Consumer Unit, yes?
In relation to choice of OCPD yes?

 

[Nigel]

That’s in relation to a Consumer Unit, yes?
In relation to choice of OCPD yes?

It is in relation to OCPD protection for RCCBs. Makes no reference to consumer units or otherwise. If an RCCB is installed then it needs to meet this reg.

 

[Deleted member 26818]

No, it doesn’t specify CUs, but it does make reference to the British Standard that applies to CUs and to the overall rating of the assembly, which suggests the assembly is ‘type tested’ and therefore a CU.

 

[Nigel]

No, it doesn’t specify CUs, but it does make reference to the British Standard that applies to CUs and to the overall rating of the assembly, which suggests the assembly is ‘type tested’ and therefore a CU.

BS EN 61439 is the Standard for Low-Voltage Switchgear and Controlgear.

Anyhow, where are you going with this point?

 

[Ian1981]

It also includes a BSEN 60947-3 isolator which also requires overload protection

 

[Andy78]

Just had a wholesaler email. Hager have responded to their interpretation of this by releasing dual RCD boards with 100A RCCBs.