Replacing Your Fuse board With A New Consumer Unit? Here Is Everything You Need To Know

A new consumer unit protects from electrocution and fire unlike older fuse boards. The latest AMD 3 units are non – combustible, contain rcds and protect a user from coming in to contact with a live conductor. In the event of current leaking somewhere it shouldn’t they protect against electrocution and fire. Older fuse boards (that is anything without an rcd device) only protect cables from becoming overloaded.  Replacing a fuse board with an AMD3 unit will help reduce the risk of electrical related injuries.


Recently Installed New Consumer Unit: Contactum full RCBO AMD3 fitted and certified: £350


Do you need a new consumer unit? Replacement is usually because customers:

1. Need a new circuit installing and their existing unit has no spare ways to connect it.
2. Want an electric shower or outdoor socket and have no rcd protection.
3. Have fault finding and a component is no longer available new.
4. Have been advised rewire-able fuse boards no longer comply with BS7671.
5. Have had loft conversion plans drawn up stating a new unit will be necessary.

Choosing a replacement unit

My advice is let the electrician you hire supply and install the new consumer unit for your home or business. They will know what is necessary for your electrical installation and any future requirements.  My first choice is a Defender model made by Contactum.  They are well made, fit well reliable and made in Cricklewood, London. All new consumer units 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 DIY job.

What to expect when your old fuse board is removed

Power for the whole property will be off whilst the work is being carried out. Your telephone line will work but your broadband equipment won’t. Most customers find it’s not the best time to be at home! If your employer allows you to work from home, bear in mind there is no power for broadband equipment and charging your laptop. The process goes something like this:

  • Ensure all sensitive electrical equipment (like computers, hi-fi and televisions) are switched off.
  • Switch the main isolator off to remove power to the fuse board being replaced.
  • Remove the distribution circuit cabling (lights, sockets, oven, shower etc) and test to ensure compliance
  • Remove the old units (sometimes there are two)
  • Fix the new unit to the wall
  • Connect the circuits up
  • More tests (prior to energizing)
  • Switch on
  • Live testing and certification

How much to have a new consumer unit installed?

The work involved depends on 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 fitting the new one. If the circuit tests come back OK the job can begin. If they don’t, the customer will know what’s necessary to resolve the faults, or re book if time is an issue. I’m an NICEIC registered electrician who can install, test and certify new consumer units in the Cardiff area from £350 .

Ten scenarios affecting the cost of replacing your rewire-able fuse board with an AMD3 unit

1. Your meter cupboard is “boxed in”. Box sections may need removing or cutting to allow the replacement enough room and space to work. The latest metal units are heavier, wider and deeper than the previous plastic ones. The hinged door (which needs to remain in place) can add another 100mm of depth. Newer properties have a lot of plasterboard walls and a secure fixing can be another issue.

Building cabinets around consumer units like this means they need to be removed to work on or in the event of replacement.

2. The original wiring isn’t long enough. Supply from the electric meter connects to the main switch inside the consumer unit; either on the left or right. The meter tails are cut to the required length at the time of original installation. If they aren’t long enough; new ones will be necessary to install your new unit.
Wiring for the circuits in your house may need extending. Different manufacturers have circuit protection in different layouts. Extending cables adds time (and the cost of wiring and connectors) to the job.


3. The earthing and bonding isn’t up-to-date.  Before any amendments or alterations are made to an electrical installation this needs to be in place. In rural areas the power supply lines enter the property overhead. In these cases you are responsible for your own (safety) earth connection. This is usually in the form of an earth rod outside the property. If the reading is too high it will need resolving prior to installing a new unit.

4. The lighting circuit doesn’t have an earth wire. Most light fittings require an earth connection. If your wiring doesn’t have one; metallic fittings and switches aren’t permitted. This is one of the biggest replacement consumer unit show stoppers.

5. The wiring for the socket circuits isn’t complete. The circuit design for socket outlets requires the wiring to be a continuous ring. This fault is common and can mean additional fault finding is necessary. The options are to find the break in the wiring (sometimes a connection in a socket outlet) or reduce the current capacity of the overload protection device.

6. The main bonding cable no longer complies. Gas and metallic water pipes need a connection back to the main earth terminal. If yours is missing or doesn’t test out OK – it will need updating.

7. The neutral and earth wire for the lighting circuit is one. This needs resolving for electrical safety and to enable rcd fitment. Older rewire-able fuse boards and miniature circuit breakers will not see this as a fault. The later rcd models do and will not stay on as long as this fault exists.

8. Residual earth leakage. Faulty appliances (and wiring) can allow current to leak (from live conductors to earth). RCDs present in the latest consumer units are designed to trip to protect, older fuse boards don’t see this. High amounts of residual current needs resolving prior to installing an rcd equipped distribution board.

9. Five circuits becomes eight. Often additional wires are added to the circuit protection since the original installation. Replacing the consumer unit is an ideal time to resolve this.

10. The location of your electric meter. Often housed in a small cupboard under the stairs making access difficult, increasing working time.

General advice for customers having a new consumer unit installed

  1. Most circuits in a domestic property now have to be protected by a Residual Current Device. When it comes to choosing a replacement unit the options are to have two rcds so roughly half the installation is protected by each one. In the event of an earth leakage fault the property will loose power to half the installation until resolved. This is the cheaper option. The other option is to have a residual device (called an rcbo) on each circuit. In this configuration in the event of a fault power will be lost for the relevant circuit. This costs more to install although it’s easier to diagnose problems and less inconvenience in the event of a fault. Worth the extra cost in my opinion.
  2. Make sure whoever installs it for you will provide certification. It is notifiable. You should receive an electrical installation certificate and building compliance. Anyone 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.
  3. Are you concerned about an up-to-date consumer unit with old wiring?  Sometimes customers ask me if its a new consumer 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 is tripping my rcd article may help you troubleshoot it yourself.
  4. Should i add or replace?  When a kitchen, bathroom or extension is renovated electricians sometimes install a second unit.  This can be to save time, not have to interfere with the original installation or down to cost.
  5. Can i fit one myself and have it tested afterwards? Installing a new consumer unit isn’t a DIY job.  The only paperwork you will get from an electrician for a DIY installation is a condition report which isn’t the same as an electrical installation certificate.

If you want to discuss having a new unit installed i would like to hear from you. Please get in touch using the form below:

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