- In a previous video,
we looked at certain requirements
in the 18th edition of "BS 7671: "The Wiring Regulations,"
that address the issue of split load boards,
as many people felt that they'd become non-compliant.
In this video, we're going to look
at the changes made in the second amendment
to those requirements,
to ask if split load boards,
like the one we've got here,
still comply.
Now the change that's prompted this video
is found in 531.3.2,
which relates to unwanted tripping
and outlines a number of things to be considered
to try and minimize this.
However, it's been adjusted,
and now for the very first time makes very specific mention
of individual RCBOs.
So let's have a look at it now
and see if split load boards are now non-compliant.
It reads, "Residual current protective devices
shall be selected and erected
such as to limit the risk of unwanted tripping.
The following shall be considered."
And we'll jump straight to indent two,
"The use of RCBOs for individual final circuits
in residential premises."
So that seems pretty solidly in favor
of RCBOs over split load RCD protection.
However, interestingly, in regulation 531.3.5.2,
which relates to the use of RCDs
for fault protection rather than additional protection,
it does state in the note there that,
"Except where particular restriction
for selectivity applies,
several circuits may be protected by the same device."
So how are we to understand
this seemingly conflicting information?
Well, the important thing to keep in mind
about regulation 531.3.2,
is that it isn't about selectivity.
It's about unwanted or nuisance tripping,
so devices operating and disconnecting circuits
when there's no reason to.
How might that happen
and how will the use of individual RCBOs
help to reduce unwanted tripping?
The main culprit in a domestic setting
is likely to be modern appliances
with electronic controls
that naturally leak some current to earth
as part of their operations,
such as washing machines, tumble dryers,
dishwashers and suchlike.
The effect is compounded
because you're likely to have several of these
on kitchen and utility circuits,
meaning that all those little leakages add up.
Is it a significant amount of current?
Well, it'll vary depending on the manufacturer
of the appliance,
but as a rule of thumb,
many appliance manufacturers will test the earth leakage
of their product.
If six milliamps or over is found,
the appliance will be sent back
for fault finding and correction.
If as much as five milliamps is found,
it will be passed as acceptable and sent on.
So three appliances on one RCD
and operating at the same time,
could immediately be leaking 15 milliamps to earth.
Couple this with other natural
but not dangerous levels of leakage from other circuits,
and the RCD could be operating and disconnecting
several perfectly healthy circuits.
So what's the solution?
Well, we've got that now familiar indent three
in regulation 531.3.2,
which used to be indent two,
and that states,
"In order to avoid unwanted tripping
by protective conductor currents
and/or earth leakage currents,
the accumulation of such currents downstream of the RCD,
shall be not more than 30%
of the rated residual operating current."
If the RCD protection has a rating of 30 milliamps
for additional protection,
then that means no more than nine milliamps of current
should be leaking to earth on the circuit, or circuits,
that it is protecting.
So if we have one RCCB protecting several circuits,
then depending on what they're feeding
we may find ourselves quickly getting over that limit.
However, does that mean that the split load board
is a thing of the past?
Not necessarily.
If there's no particular restriction for selectivity
and we've broken down how to minimize selectivity issues
on split load boards
in one of our CPDs on the Know How page at efixx.co.uk,
then you could consider having RCBOs on circuits
that are likely to experience high earth leakage currents,
such as socket circuits and induction hubs,
and a couple of RCCBs
protecting the other circuits in the house
that have much smaller earth leakage currents,
like lighting and things like that.
The use of dual RCD boards only,
will limit the future-proofing of the property,
meaning boards may need replacing sooner.
But having a dual RCD board with some,
what we could call,
high integrity circuits protected by RCBOs,
gives us options for rearranging circuits in the future.
So clearly the Regs are indicating
that it is best practice to have individual RCBO protection
to circuits that require it,
and possibly a hint at future editions
categorically stating that split load boards
will no longer be acceptable,
but we're not there just yet.
Who knows, maybe the 19th edition
will finally outlaw split load boards.
We'll have to just wait and see.
If you've enjoyed this video,
please check out this one here.
Or for a full breakdown of the changes amendment two
made to circuit protection,
check out our free training package
by clicking the link in the description below.
Thank you very much for watching.