Safety update; RCBOs supplying inverters or storage batteries
BEAMA have issued a safety update (March 2024) regarding the use of RCBOs to connect PV inverters or storage batteries.
This is not yet part of the IET Electrical Wiring Regulations, but it is sufficiently serious that an amendment is being expedited.
Overview: household electrical circuits are wired from a Consumer Unit which contains a number of trips.
Most trips are there to prevent excessive current being passed through wires/cables. Those are MCBs (Miniature Circuit Breakers).
It is common for a consumer unit to have one or more RCDs (Residual Current Detectors).
These compare the outgoing current on the Live wire, with that being returned on the Neutral.
If there is an imbalance, the contacts will open to prevent fire or electric shock to someone who has touched a live cable.
Increasingly, electricians are fitting RCBOs for individual power circuits.
These combine the functions of an MCB and RCD.
They will open the contacts either for over-current, or because current is leaking away somewhere.
If a single-circuit RCBO trips out, then at least the lights remain on so you can see what's gone wrong!
RCDs and RCBOs both have a test button.
This should be pressed periodically to check that it will open the contacts to protect against electric shock
When solar panels or storage batteries are installed, it is not mandatory that the circuit is supplied from an RCBO. An MCB is sufficient.
However, many installers do use an RCBO to provide an extra level of safety for when it might be necessary for an inverter to undergo maintenance.
Most Solar Inverters and Storage Batteries are "Grid tied".
They export to the mains supply through the same wires which connect them to the consumer unit.
A grid-tied inverter will have a G98 certificate, and requires permission from the regional DNO to install it.
This common arrangement means that electricity will pass through the RCBO in either direction.
The RCBO contains a small amount of electronics to handle the current sensing.
When there is a fault (either over-current or earth-leakage) a solonoid is energised (switched on), which opens the contacts.
If the RCBO was on a normal power circuit, opening the contacts would remove power from the electronics.
The trip would remain open until the lever was manually moved, and the solonoid would no longer be powered-on.
But if there is power still being applied in the reverse direction by an inverter or storage battery, when the contacts open, the solonoid remains energised.
Such a small solonoid will overheat and burn out.
The circuit can still be re-powered using the lever, but it will no longer be able to protect against electric shock.
The home owner won't know that.
The solution is to use a an RCBO specifically designed for bi-directional use.
A bi-directional RCBO has a third pair of contacts.
When the solonoid operates to open the trip, that 3rd contact set removes power from the electronics, and the solonoid coil is de-energised, preventing burn-out.
How can you tell if an RCBO is bi-directional?
Most RCBOs have arrows to show the direction of current, or have a label which denotes Supply and Load terminals.
A Bi-directional RCBO will not be marked for Supply and Load.
It may also have a set of arrows pointing in both directions.
If an RCBO isn't marked as being bi-directional, then it isn't.
The IET Wiring Regulations aren't retrospective.
When the amendment is released which specifies the need for a bi-directional RCBO, there will still be many thousands of installations which appear to have an operational RCBO, but it will only offer protection against over-current. It won't be acting to prevent fire or avoid electric shock.
It is up to forum members here to spread the word to others and advise that an existing RCBO is exchanged (by an electrician!) for a bi-directional type.
Save energy... recycle electrons!
This photo shows a bi-directional RCBO by Proteus at Redditch.
The symbols are correct, and the third-contact which the solonoid switches is visible in the diagram on the side.
What I still don't like is:
- the terminals being labelled 'In' and 'Out'
- no bi-directional symbol or marking on the part of the RCBO which remains visible to the householder after installation is completed
This particular RCBO is Type A
and Curve C... which defines the time it takes to trip due to over-current.
Most household MCBs and RCBOs are curve-B, which operates faster.
I use Curve-C trips to supply circuits which are likely to have large inductances connected (motors in a workshop or an inverter).
Update 28may24:
I have a response from Proteus Switchgear to say that they are already acting on the BEAMA directive and "will remove the in/out and also add on a bidirectional arrow symbol to the front of compliant devices"
The changes will filter through once existing stocks have been exhausted.
Save energy... recycle electrons!
- 26 Forums
- 2,136 Topics
- 46.8 K Posts
- 32 Online
- 5,662 Members
Join Us!
Podcast Picks
Latest Posts
-
RE: Rodents! A word of warning for heat pump owners
The gaps and holes have reduced on heat pumps over the ...
By dgclimatecontrol , 2 hours ago
-
RE: Ecodan & MelCloud scheduling
I couldn't agree more. I might go so far as to change t...
By Majordennisbloodnok , 2 hours ago
-
RE: Air source heat pump roll call – what heat pump brand and model do you have?
Forum Handle: EGP01 Manufacturer: Samsung Model: 8K...
By EGP01 , 5 hours ago
-
Thanks for the heat geek info. I've fitted my own heat ...
By bontwoody , 6 hours ago
-
RE: Does anyone have experience of a smart water meter?
Just to give a sense of scale, I've used the CCW water ...
By Majordennisbloodnok , 7 hours ago
-
-
RE: Powerwall 3 or Myenergi or something else?
We have a Tesla Powerwall 3, recently installed, so I m...
By Old_Scientist , 1 day ago
-
RE: Mitsubishi PAR-WT60R-E Wireless Controller installation
@morgan They have been paired once but it was thought b...
By DavidAlgarve , 2 days ago
-
RE: Isolating the system for a planned power cut
A great many ground-mounted local substation transforme...
By Transparent , 2 days ago
-
RE: Heat Pump Servicing & Maintenance – Good Value or Rip-Off?
Having bit the bullet and paid £250 for a service, our ...
By Old_Scientist , 3 days ago
-
New heat pump heating system underperforming in Italy... Advice needed!
hi all, first post! I've just renovated a house in sout...
By robinlawrie , 3 days ago
-
RE: Anyone still weathering it out with Agile?
I went to Agile when I had solar installed July last ye...
By NJT , 4 days ago
-
RE: Mitsu Wireless Controller and MelCloud
Well it has now become obvious that the installation of...
By DavidAlgarve , 4 days ago
-
RE: Say hello and introduce yourself
Whilst you're busy installing services (pipes and wires...
By Transparent , 5 days ago
-
RE: New Vaillant aroTherm Plus in black - When will it come to the UK?
@editor I know it was formally announced at Ish the oth...
By PatrickVito , 6 days ago
-
@moman0311 welcome to the forums. I've received your em...
By Mars , 6 days ago
-
RE: Thermostat for Ideal Logic Air with 3 zone support
No harm at all in plumbing it as 3 zones, I would have ...
By JamesPa , 1 week ago
-
RE: ASHP heat output monitoring
@carlo I see there is a discussion in Facebook user gro...
By Tim441 , 1 week ago
-
RE: Flexi-Orb Heat Pump Scheme: A Game-Changer for the UK's Heat Pump Industry
MCS have set a potential trap in the new version of MCS...
By JamesPa , 1 week ago
-
RE: Who has a V2G EV installation
General comment on battery care... I guess if ev is on ...
By Tim441 , 1 week ago