RCBOs on an RCD'd mainswitch

[DomB]

Hi,

If I had a CU with an RCD'd main switch and put in a new circuit on an RCBO, would the RCBO always be the first to trip should there be a fault on that circuit?

Thanks!

 

[1shortcircuit]

They are. Hifly (I think) is talking about in the event of a residual current fault.

Please excuse my lack of understanding. On a TT system, why would this be more advantageous over an RCD or RCBO?

:thumbsup

 

[topquark]

Please excuse my lack of understanding. On a TT system, why would this be more advantageous over an RCD or RCBO?

:thumbsup

It wouldn't if they had decided to go with your earlier suggestion and replace ALL of the circuits with RCBO's then it wouldn't be a benefit.

However the discussion at that point had moved onto using a mix of MCB and RCBO (some of the MCB's being protected by RCD, some not).

On a TT system having the 100mA up front RCD will afford a degree of protection if the usual max Zs for the unprotected circuits is not met).

Remember that on a TT system the Ze (Ra) is usually not that stable, so having the backup of the upfront RCD is seen to be advantageous.

Keep in mind there are some circuits (smoke alarms are a good example) that are better not to be protected via 30mA RCD (so they loose supply when other circuits cause a trip). Even if the smokes are on an dedicated RCBO protected circuit then the risk is, a fault in one unit will take all of the smoke alarms off main power. This is why a lot of folk prefer to use the rechargeable battery backup ones rather than dry cells (or mains only).

 

[richy3333]

Thanks all. Agreed re the customer trying to dictate what's done; I just wanted to be able to put him straight without any come-back.

It is a TT system, yes - spotted!

I'd rather not do RCBO's all round mainly cos of the cost.

I was going to keep it simple, get a 17th edition dual RCD CU (15 Way Dual RCD + 100A Mains Switch) and split the circuits wisely across the two.

He's calling for RCBOs for his alarm & heating circuits. I can see his point - should he be away and something trips the main RCD which affects his alarm circuit then that might not be best..

grateful for your advice chaps

Denmans do a 14 way RCBO Cu with 8 RCBO's for £99. Any good for you?

 

[Marvo]

Denmans do a 14 way RCBO Cu with 8 RCBO's for £99. Any good for you?

Wow, that sounds very very cheap.

 

[1shortcircuit]

Denmans do a 14 way RCBO Cu with 8 RCBO's for £99. Any good for you?

Damn, be lucky to get 4 Wylex RCBO's by themselves for that kind of price?

 

[Amp David]

Denmans do a 14 way RCBO Cu with 8 RCBO's for £99. Any good for you?

Shame theres not a Denmans near to me!

 

[Marvo]

Shame theres not a Denmans near to me!

That price sounds too good to be true, anyone know what kinda quailty they are?
Shame there's not one near me either

 

[topquark]

That price sounds too good to be true, anyone know what kinda quailty they are?
Shame there's not one near me either

I did get a dogalogue through the door a couple of weeks ago, I'll see if it's still around and has any more details. It may have been "filed".

 

[richy3333]

Shame theres not a Denmans near to me!

? David - there's one in Mac? Denmans ship stuff to me up in Scotland

 

[richy3333]

That price sounds too good to be true, anyone know what kinda quailty they are?
Shame there's not one near me either

The branch I deal with say they can't meet demand for them. I think they'll be made for Denmans by someone else and rebranded. Possibly (but I'm guessing) someone like MK et al. Seem fine to me and sometimes the customer just won't pay for a decent Hager board.

In a similar vein Denmans do their own electric heaters which are made by Dimplex

BTW I'm not connected to Denmans in any way, it's just that sometimes they sell products that met a particular price point for the customer and the products are better than Wylex or similar (my opinion).

 

[Marvo]

The branch I deal with say they can't meet demand for them.

That doesn't surprise me, where I am we pay the same price for a 14-way box with a main isolator and a few mcb's in it.

 

[richy3333]

This is the last ad I can find, so it looks like the price has come down a bit

By the side of it they are doing a 12 way dual RCD board for £54 - which is interesting as in another thread someone was mentioning a Wylex board for £45? I've fitted a few of these and they are very similar to MK stuff.

Hope this helps

 

[richy3333]

That doesn't surprise me, where I am we pay the same price for a 14-way box with a main isolator and a few mcb's in it.

Ouch, that sounds rough mate, though I guess it's 'horses for courses' - I've recently fitted a couple of 10 way Hager boards populated with RCBO's and they worked out to be around £300 each (customer is in the music business so can afford quality equipment).

 

[Amp David]

? David - there's one in Mac? Denmans ship stuff to me up in Scotland

And in Trafford park, but nevers seem worht while doing a 40 - 50 mile round trip to get materials