Fuse board replacement
A new consumer unit helps prevent electrical injury and fire unlike older fuse boards. AMD 3 units protect against accidental contact with a live conductor thanks to rcd protection. Older fuse boxes (anything without a rcd device) only protect cables from becoming overloaded.
Do you need a new consumer unit? Typical reasons for replacement:
- You need a new circuit installing and your fuse board has no spare way.
- You want an electric shower installed and have no rcd protection.
- Parts for the existing unit are no longer available new.
- Rewire-able fuse boards no longer comply with BS7671.
- Loft or kitchen plans list new circuits and a new unit will be necessary.
Choosing a replacement fuse board: my advice:
Pay the electrician to supply and install your one. Popular choices from MK, British General, Hager and Wylex. I install Defenders made by Contactum. Well made, reliable and made in the UK. AMD3 models should:
✅ Be Type tested to BS EN 61439-3
✅ Comply with BS7671 and come with an electrical installation certificate
✅ Comply with Part P of the building regulations (notifiable work)
✅ Fitted by a professional electrician (it isn’t a D.I.Y job)
✅ Have enough spare ways for existing and any future circuits
What happens when your electrician replaces your fuse board
Power for the whole property will be off. Your telephone line will work but your broadband equipment won’t. Customers find it’s not the best time to be at home! The process goes something like this:
Switch off sensitive electrical equipment (computers, hi-fi and televisions).
Switch the main isolator off removing power to the fuse board.
Remove the consumer units wiring for lights, sockets, oven, shower etc. Test to ensure compliance.
Remove the old unit(s)
Fix the new one to the wall
Re-connect the wiring
More tests (prior to energizing)
Switch the power on
Live testing and test results
The cost of replacing a consumer unit
This will vary depending on where you live in the UK. Other factors include its location, the number of circuits and existing wiring. Arriving with a replacement and starting the job means banking on no problems. Most electricians recommend testing prior to replacement (more so on an older Cardiff property). If the results aren’t good; the customer will know what’s necessary to resolve them. I’m an NICEIC registered electrician who can install, test and certify new consumer units in the Cardiff area. Prices start from £350 .
Some scenarios affecting the cost of replacing your fuse board
Boxed in. Box sections may need removing or cutting to allow replacement. The latest consumer units can be heavier, wider and deeper than previous plastic models. The hinged door can add 100 mm of depth. New builds have a lot of plasterboard walls and a secure fixing can be an issue.
The wiring isn’t long enough. The supply from your energy providers meter will connect to the main switch inside your new unit. Meter tails cut to the required length at the time of original installation might not be long enough. If so, new ones will be necessary adding to the cost of your new AMD3 model. The wiring supplying your lights, sockets, shower etc may need altering. Up-to-date models can be larger than previous units requiring a different location. Consumer unit manufacturers have circuit protection in different layouts. Extending wiring adds time and consumables.
Earthing and bonding isn’t up-to-date. This needs to be in place before any amendments or alterations. Domestic properties in South Glamorgan have metallic gas pipes. Water pipes in older parts like Cathays, Roath and Splott isn’t uncommon. In these cases they need to be connected to the consumer unit via a thick, green and yellow cable. If you don’t have one or it doesn’t test out OK; it will need updating. Power lines can enter the property overhead in rural areas. Home-owners need to make arrangements for their own earth connection. An earth rod outside the property being the usual way to resolve this.
The lighting circuit doesn’t have an earth wire. Most light fittings require an earth connection. If your consumer unit wiring doesn’t have one; metallic fittings and switches aren’t permitted.
The wiring for the socket circuits isn’t complete. The circuit design for socket outlets requires the wiring to be a continuous ring. A common occurrence requiring additional fault-finding.
A combined neutral and earth wire on the lighting circuit. Older non-rcd fuse boards will not see this as a fault. The later models do and will not stay on as long as this fault exists.
Residual earth leakage. Faulty appliances (and wiring) allow current to leak from live conductors to earth. RCDs present in the latest AMD3 consumer units will trip removing the power to protect us. Fuse wire and miniature circuit breaker boards don’t see this fault not being designed to do so.
Five circuit breakers can become eight. Additions over time can mean several circuits connect to one breaker. Replacing with a larger consumer unit will resolve this.
The location of your electric meter. Restricted access will increase working time and cost.
My advice if you need a replacement
Most circuits in a domestic property need rcd protection. AMD3 models have two options: 1. Split the installation in half with two rcds. In the event of an earth leakage fault (causing one rcd to trip); property will lose power to half the installation until resolved. This is the cheaper option. 2. A consumer unit with rcbo’s on each circuit (each device protects one circuit). This costs more to install although easier to diagnose problems and less trouble in the event of a fault. Worth the extra cost in my opinion.
Make sure whoever installs your consumer unit provides paperwork. You should receive an electrical installation and building compliance certificate. Electricians on the competent person register will be able to do this. Without it you might come unstuck in the event of an insurance claim or if you decide to sell.
Concerned about installing an up-to-date consumer unit with old wiring? Customers ask me if it’s a new unit they need or a complete rewire. It’s wise to have the installation tested to get an overall picture of the installation. If your new unit trips my rcd article may help troubleshoot before calling an electrician.
Add or replace? Renovating a kitchen, bathroom or extension can mean a replacement or additional consumer unit. Adding can save time and not interfering with the original installation can be the cheaper option.
Can I replace my own fuse board and have it tested once finished? Swapping out a fuse board isn’t a DIY job.
If you live in the Cardiff area and need new consumer unit installing; please get in touch. You can expect a reply within twenty-four hours.