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What is Part P? | What is an RCD?

What is Part P?

Introduced in January 2005, Part P is a section of the Building Regulations that specifically relates to electrical safety. It is one of a number of official documents (Parts A, B, C, E, F, L, M & P) that each relate to a defined area of buildings, their construction and their safety.

It is not a part of the Wiring Regulations and does not conflict with them. It does, however, extend them to embrace the Building Regulations.

To the householder, it has major implications, defining who can do electrical work and where they can do it. It requires that all but the most minor electrical works be notified to local authority building control departments. It also defines 'special locations and installations' and they are kitchens, bathrooms and all outdoor installations plus some others. Any alterations or installation works in special locations are notifiable.

Essentially, the only work that can be done by a DIYer without notification and subsequent test and inspection by building control is to replace like for like, e.g. a light fitting or socket outlet. A competent or Part P qualified person can carry out all other work but must still inform (and pay) building control before work commences. Only persons Part P qualified AND registered with an authorised self-certification scheme (e.g. NAPIT, NICEIC and others) can carry out the work without prior notification or any payment to building control.

It also requires that any electrical works carried out have to conform to all other parts of the building regulations. Examples of these requirements are:

Any competent electrical installer should be able to demonstrate knowledge of the requirements of Part P and be able to explain these to customers in plain terms.

What is an RCD?

RCD stands for residual current device, a name that gives very little away. However, it is an important safety device with a specific purpose and that is to protect YOU, the person, rather than the electrical installation.

It is worth taking a step back here to look at where an RCD fits into the scheme of things.

All households will have, somewhere, a distribution board. These are also known as fuse boards, consumer units, or 'the thing that crackles and smoke comes out of sometimes!'

A distribution board is the point in the house where the raw electrical power comes in after being metered for usage. The household installation is divided into a number of different circuits, each circuit protected by a safety device. Originally, and still in many older properties, this device was a re-wireable fuse; a bakelite slab which could be pulled out from the board to have a new piece of fuse wire screwed in if it had blown... a great inconvenience to the householder and a nightmare to the electrician trying to find a fault! In more modern installations these devices are MCBs, which stands for miniature circuit breaker. These have the convenience of being controlled by an easily operated toggle type switch on the front and, unlike their predecessors, cannot be tweaked' with some heavier duty fuse wire! Old or new, fuses and MCBs have different current ratings, specified in amps; typically for fuses these are 5, 15 and 30 and MCBs 6, 16, 32, or 45 (with a few more values available and in use).

Contrary to popular belief, the main purpose of these devices is not to protect us, the consumers, but to protect the cables running throughout the household. The different circuits in the house have different sizes of cable to cope with the amounts of electric current flowing in them. Too much current will cause overheating, melting of the insulating sheathing and all the associated fire risks. The fuse or breaker ensures that excessive current will not flow in the cable by blowing or tripping out if that circuit's current rating is exceeded. These breakers provide over-current protection.

The fatal level of electric current to the human being is 50 milli-amps. That is one twentieth of one amp. So a 6 amp MCB will allow at least 120 times the fatal level of electrical current to flow before it trips!!

Now, in geography all roads may lead to Rome, but in the electrical world all roads lead to earth. Electricity will always flow to earth given the chance and if a person is unlucky enough to present a path to earth from a live conductor, a severe electric shock will occur.

This is where the RCD comes in. In a normally operating circuit the current flow is balanced between the live and neutral. An RCD will detect a sudden change in this balance, i.e. if current is flowing to earth via a different path. If this imbalance exceeds a certain level the RCD will trip out. In most RCDs in the home this level is 30 milli-amps, under the level of fatality and the trip will operate in a fraction of a second. It can be seen that the RCD is a very important lifesaving safety device.

In practical usage, the RCD is usually combined with an over-current MCB (as described above) and is more correctly described as an RCBO (residual current circuit breaker with overload). This is the device that consumers will find in their distribution boards.

The latest wiring regulations require that any new installation has to have RCD protection on every circuit. This is usually achieved by splitting the circuits into two groups, each group having a master RCBO. So if a fault occurs and one RCBO trips, the other group of circuits will remain on giving lights and power to at least half the household. Our own recommendation to anyone having a rewire or board updating is to have an RCBO on every circuit so a fault will only take out one circuit.

There are many households with older electrical installations that do not have any RCD protection at all. Electricity is a great servant but it is dangerous. You cannot see, smell, hear or taste it but, believe me, you CAN feel it!

On the downside, nuisance tripping can occur, a light bulb popping can cause a trip as can old washing machines, freezers and fridges. But overall, an RCD tripping out will indicate a problem and they DO SAVE LIVES!

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