RCBO Type

[Oracle]

Hello again.

What is everyone's opinion on whether the type (B,C) is important for domestic situations?

Oracle.

 

[kme]

As long as you can meet the Zs values for a C curve, it`ll make little difference.

I`ve used `em a few times - Wylex don`t seem to have availability on B curve RCBO`s!!!

KME

 

[ian932]

You may struggle to acheive max EFLI on TN-S on type c above 20A due to possible higher Ze (max 0.8ohm) but other than EFLI issue there is no reason for not using either IMO

 

[Evans Electric]

The only reason for a type C for domestic is , AFAIK to avoid tripping out when lamps blow, but need one eye on the Zs.

 

[Oracle]

what happens if it is a tt system (high elfi) - when using rcbo's? You don't fit a td incomer, as everything is individually protected.

O.

 

[Oracle]

In addition to the above...

More I think about maybe you do still have to fit a TD incomer? Or will a simple switch isolator suffice if everything is RCBO'ed?

O.

 

[Shamus]

Not too sure what you're getting at with that question, but i've just recently bought a large sliding compund saw, with a 2.3kw motor. When i tried starting it, the 16A breaker in my shed tripped, along with the main 20A breaker in the CU in the house. Both breakers were type B. The start up current must have exceeded 20A for it to take out both breakers.

I've changed both for type C's and the problem has gone away.

Not sure if this is what your asking, but under normal circumstances i doubt if you would ever notice the difference.

 

[SPECIAL LOCATION]

Not too sure what you're getting at with that question, but i've just recently bought a large sliding compund saw, with a 2.3kw motor. When i tried starting it, the 16A breaker in my shed tripped, along with the main 20A breaker in the CU in the house. Both breakers were type B. The start up current must have exceeded 20A for it to take out both breakers.I've changed both for type C's and the problem has gone away.

Not sure if this is what your asking, but under normal circumstances i doubt if you would ever notice the difference.

Hello Shamus welcome to the forum...Guiness Drink

Just a simple question.. are your Zs values still ok?

typically the type 'C's are about half that of type 'B'..

e.g.

20A b= 2.3ohm c=1.15ohm

16A b=2.87ohm c=1.44ohm

this would obviously affect the max permissible cable length..

and when you say shed......... is it a long way....

But saying that.... Is it RCD protected anyway? so Zs of less importance.

I think the point the original poster was getting at was generally on domestic we use type B mcb's (as stated higher Zs permissible), but since 17th with added RCD & RCBO's.

Many manufactures only tend to do type C RCBO's.

which is why Oracle was asking for opinions on Type B -vs- Type C

HTH!

 

[batty]

As long as you can meet the Zs values for a C curve, it`ll make little difference.I`ve used `em a few times - Wylex don`t seem to have availability on B curve RCBO`s!!!

KME

Martyn my wholesaler has no problem getting b type wylex rcbo's. I needed a

20 amp the other day they had 20 on the shelf. They mainly do wylex boards though rather than other makes.

 

[batty]

Hello Shamus welcome to the forum...Guiness DrinkJust a simple question.. are your Zs values still ok?

typically the type 'C's are about half that of type 'B'..

e.g.

20A b= 2.3ohm c=1.15ohm

16A b=2.87ohm c=1.44ohm

this would obviously affect the max permissible cable length..

and when you say shed......... is it a long way....

But saying that.... Is it RCD protected anyway? so Zs of less importance.

I think the point the original poster was getting at was generally on domestic we use type B mcb's (as stated higher Zs permissible), but since 17th with added RCD & RCBO's.

Many manufactures only tend to do type C RCBO's.

which is why Oracle was asking for opinions on Type B -vs- Type C

HTH!

SL this is why I always put adequate supply into garages and outbuildings at least 32 amp that way you can put ring main for sockets or 32 amp radial.

Batty

 

[SPECIAL LOCATION]

SL this is why I always put adequate supply into garages and outbuildings at least 32 amp that way you can put ring main for sockets or 32 amp radial.Batty

Indeed there sir Batt's!

I got a job with a customer who has a log burning stove fire,

(very common & fashionable nowadays),

and in his shed he has one of those electrically operated log cutter things...

That takes quite a chunky current surge as start-up!!

about 15m from house end of garden!!!

you can find some quite hefty power tools in some sheds & external garages.

 

[Oracle]

the reason for the question is 2 fold:

On a tt system the zs is too high for any breaker (normally) so to mitigate this you use an rcd - therefore is the type of rcbo relevant anymore?

The second part. If the tt board is using rcd's and rcbo's does the main isolator need to be a time delayed rcd or can it be a simple isolator?

6.

 

[batty]

the reason for the question is 2 fold:On a tt system the zs is too high for any breaker (normally) so to mitigate this you use an rcd - therefore is the type of rcbo relevant anymore?

The second part. If the tt board is using rcd's and rcbo's does the main isolator need to be a time delayed rcd or can it be a simple isolator?

6.

Oracle

If it is full of Rcbo's or a 17th edition insulated enclosure as long as all circuits have Rcd protection that is fine on tt just to have a double pole or 4 pole on three phase isolator.

Batty

 

[Shamus]

Hello Shamus welcome to the forum...Guiness DrinkJust a simple question.. are your Zs values still ok?

typically the type 'C's are about half that of type 'B'..

e.g.

20A b= 2.3ohm c=1.15ohm

16A b=2.87ohm c=1.44ohm

this would obviously affect the max permissible cable length..

and when you say shed......... is it a long way....

But saying that.... Is it RCD protected anyway? so Zs of less importance.

I think the point the original poster was getting at was generally on domestic we use type B mcb's (as stated higher Zs permissible), but since 17th with added RCD & RCBO's.

Many manufactures only tend to do type C RCBO's.

which is why Oracle was asking for opinions on Type B -vs- Type C

HTH!

Yes the Zs valuse are ok. The run to the shed isn't that far away and it is rcd'd. I will hopefully be building a new double garage in the near future, and i intend upgrading the entire supply to the garage, and provide a suitable supply for external electrics as well, (maybe a hot tub - if the cost of electric ever comes down.)

 

[Nicky Tesla]

Type B or C has nothing to do with Zs when used with an rcd or rcbo because the curves are to do with overcurrent protection along live and neutral wires not earth wiring. The Zs on a 30mA rcd can be up to 1666ohms. It is preferred for the Zs to be in normal parameters but it is not essential.

 

[Nicky Tesla]

Does a DB in a TT system need a time delayed rcd if all the mcbs are protected by other rcd and rcbos down to 30mA?.....Of course not, what purpose would it serve. I think you knew that anyway really but just needed conformation

 

[batty]

Type B or C has nothing to do with Zs when used with an rcd or rcbo because the curves are to do with overcurrent protection along live and neutral wires not earth wiring. The Zs on a 30mA rcd can be up to 1666ohms. It is preferred for the Zs to be in normal parameters but it is not essential.

Nicky your phase to neutral will still need to be below tables in regs though to ensure mcb part trips within required times.

Batty

 

[Tarpole]

Well said . Although the correct figure is now 1667 , but lets not split hairs

 

[Apache]

Well said . Although the correct figure is now 1667 , but lets not split hairs

we decided it's 1666.666666666666666666

so it's a rounding issue

 

[Andy™]

we decided it's 1666.6666666666666666667so it's a rounding issue

you gotta round the last number to 7 patch