RCBO trips RCD

[Tazer]

Hi

Got a slight issue.

I have an RCBO for the Smoke Alarms on a 17th Edition CU.

As the CU has two Neutral bars, the Smoke alarm RCBO was connected to the first neutral bar same as the first RCD set.

The issue is as soon as you switch on the power it trips the RCD, which makes sense due to the imbalance

Is it possible to have or purchase another Neutral bar for a Wylex consumer unit so that another bar can be added for any RCBOs before the RCD.

I have about 4 RCBOs before the RCD.

 

[MalcofArabia]

Is the RCD protecting cb's I'm assuming.

What is your board configuration 2 rcd's I assume and a double pole switch.

Your RCBO's should be on the non protected side. This means that after the main switch and before the RCD's. Most boards you can configure to do that by moving things up and down on the bus bar. So you take out all your RCB's move the RCD's along away from the main switch and the gaps you have left will be the non protected side where you can fit the RCBo's.

Just out of curiosity why have you got so many RCBO's ? You do know that an RCBO is a CB and RCD combined and if you use them you don't need to RCD protect them.

You also need to know that as you are altering the CU you will need to write out an EIR for this work under Alteration.

 

[MalcofArabia]

Sorry meant an EIC not an EIR as that does not exist

 

[Tazer]

Hi,

Well, I have two consumer units. One in the loft and the main one downstairs.

The loft has one RCBO which is the Smoke Alarm
Downstairs has 3 RCBOs, Garden Shed, Steam Shower and House Alarm.

They all sit before the RCD (first) one.

But the problem is the CU only has two Neutral bars, so when you connect the blue fly lead to the first neutral bar, the same bar the RCD and all other items are connected, the RCBO trips.

The only way around this I think is by having a seperate Neutral bar just for the RCBOs

 

[MalcofArabia]

Ok the one in the loft with the single Smoke alarm RCBO what is actually in that unit, cicuit wise?

How are you feeding the loft CU? I'm assuming that this is a second board the main board is down by the meter head??

 

[JohnD]

it would be very useful to see a photo of the connections inside your CU

 

[Tazer]

At work at the moment so will not be able to take pics till later tonight.

Thats right, two CU, main CU is near the meter head downstairs.

The loft unit is powering all the loft. SWA 16mm cable brought up from downstairs which consists of main head going into an isolater. Isolater then goes to a 100amp junciton box (Henleys Block). One goes to the main CU, the other to a 60amp switch fuse where the SWA cable goes into.

Both CU are 17th edition with 2 RCDS and double pole switch (Wylex)

How does one normally connect an RCBO? where does the neutral fly lead go

 

[JohnD]

the neutral flylead of an RCBO goes to a neutral bar which is straight off the isolator and has not passed through an RCD

exception would be if it was a time-delayed RCD and an instant RCBO, but even this is doubtful since RCBOs are almost always single pole, so an N/E fault would trip even a delayed RCD

If you are using RCBOs it is more usual to feed them from an isolator, and have an RCD for the non-RCBO circuits

 

[Chri5]

Have you tried (AS A TEMPORARY TEST) wiring the rcbo neutral direct to the neutral on the switched side of the mains isolator in the CU.

Something that can't be permanent, but will prove if the RCBO trips due to imbalance, is faulty or works correctly.

Can't remember what the terminal rails are called, pretty sure there's a conversion pack which includes rails and neutral leads, have looked at Wylex web site and can't find

See old library picture for sort of arrangement required-->

Untitled

• Chri5
• 19 Feb 2009
• 4

I'll sort out the poor factory terminations on the neutrals tomorrow. I need to find my...

 

[Tazer]

Yes that what my conclusion was too.

But the problem is, having 2 RCDs and fly leads being connected to each Neutral bar from RCD were are you suppose to put the neutral fly lead for the RCBO unless you have 3 neutral bars.....

 

[JohnD]

you aren't. A CU with two RCDs is designed in the expectation that MCBs will be fitted, not RCBOs.

Chri5's pic shows one way of doing what you need

 

[LiamPope]

You need a short piece of neutral bar and another neutral fly lead, then shuffle things around to fit it. This was available as a seperate kit for my hager CU for a few quid - I'd expect similar to be available for wylex.

 

[ban-all-sheds]

According to this: //www.diynot.com/forums/viewtopic.php?t=232987 you've had an electrician involved.

Did he install this RCBO?

Or did you, despite this little episode showing that you don't know anywhere near enough to be messing with things like this?

 

[Tazer]

Your right.

It was finalised this Friday and he signed off the paper work. Also mentioned to wait 2-3 weeks where I will get some sort of certificate. He done all his testing etc etc.

I only noticed the problem last night when I switched on the RCBO as it was off, thats when the RCD tripped.

I phoned the guy straight away and he will pop down on Friday when I have a day off from work.

The problem he mentioned which I conculded as well was the Neutral bar. As in the pic above that clearly shows 3 Neutral bars, my CU only has 2.
Hence I was doing my homework

 

[ban-all-sheds]

Oh dear.

1) He should have known right from the start that he couldn't install an RCBO in that CU. He is ignorant and incompetent, and you should be worried about that as ignorance and incompetence with electrical work can be very dangerous. I wonder what else he might have *****d up?

2) His testing was clearly inadequate - either more ignorance and incompetence, or sheer laziness. More reasons to be worried about what other ****-ups he's left behind.

Have you paid him?