New consumer unit on old wiring? It can get EXPENSIVE!

1. What even is a consumer unit?

Where the electricity comes in to your home you'll find your meter and after the meter you will find your consumer unit. The consumer unit is the box that distributes electricity around your home and in larger properties you may have multiple consumer units. For example, you might have a separate garage consumer unit or perhaps a separate home office consumer unit. 
If you have a meter box on the wall outside your home, your consumer unit is often located close by on the inside but that's not always the case!

2. What is a fusebox?

A fusebox is the 'old time' name for a consumer unit. A fusebox used to quite literally be a wooden box and the outgoing circuits were all protected by fuses or fuse wire.

Ultimately, fusebox, fuseboard, consumer unit, distribution board etc are just all difference ways to call the box on your wall that sends the electricity around your home.

3. What's the difference between a fusebox and a consumer unit?

Not a lot really. Both fusewire and miniature circuit breakers are for 'overload protection'. This basically means they will trip or blow before the wiring is overloaded and becomes a fire risk. 
The modern Consumer Unit comes with RCD protection which is now regulation to install for practically all circuits in a domestic property, some exclusions do apply. An RCD (Residual Current Device) is far more sensitive it's purpose is to stop you getting a fatal electric shock in the event of an electrical fault.

4. Old wiring with a new consumer unit?

Electrical guidance suggests that electricians should always carry out an electrical installation condition report BEFORE a fusebox is replaced for it's modern counterpart. Old wiring sometimes may not have a reliable earth on the circuits or even no earth at all! This was common in lighting circuits 50+ years ago. 
Having an EICR carried out will give you an understanding on the condition of the electrical installation. If it has degraded a lot or has various other electrical faults then the new RCD's may trip out as they are much more sensitive.

5. How much does a consumer unit upgrade cost?

That depends entirely on who the electrician in. For a full upgrade including an Electrical installation condition report before the upgrade you can be looking at anywhere from £850-£1400.

What's worse, is that it can become EXTREMELY expensive if your electrician doesn't do the EICR first. If your electrician just changes the board without the electrical test first you could be left with tripping electrics and a bill for countless hours of fault finding work, or even worse, no electric and an electrician who has said you need home re-wiring carried out which can cost in the THOUSANDS!

Always check you're getting an EICR before the fuseboard upgrade and always use a registered, reputable electrician.