circuit protection electrical circuits require protection to prevent fire or electrocution in the...

Circuit Protection

• Electrical circuits require protection to prevent fire or electrocution in the event of a fault. There are two main types of circuit protection used RCD’s and MCB’s.

(RCD) Residual Current Device

• Is an electrical wiring device that disconnects a circuit whenever it detects an imbalance of 30mA or more between the energized conductor and the return neutral conductor. An imbalance may indicate current leakage through the body of a person who is grounded and accidentally touching the energized part of the circuit. A lethal shock can result from these conditions. RCCBs are designed to disconnect quickly enough to prevent injury caused by such shocks. They are not intended to provide protection against overcurrent (overload) or short-circuit conditions.

Rewire-able Fuse

• These are an older form of circuit protection, but are still often encountered. They use a short length of wire that will over heat and burn through if too much current is drawn through the circuit. The fuse takes much longer to function than a MCB which could lead to fire or electrocution before the fuse would burn out. Care should always be taken when encountering this type of fuse as it is very easy to fit them with a larger size of wire than they should.

(MCB) Miniature Circuit Breaker

• A MCB replaces a rewire able fuse. MCB are more sensitive and therefore safer than the older type of fuse. Modern MCBs contain 2 trip mechanisms, one thermal, one magnetic.

• The thermal element is slow acting, and responds to sustained overload currents of at minimum 1.13-1.45 x rated current.

• The magnetic element responds rapidly to substantial fault currents.

• Once tripped the fault should be found and rectified before resetting the MCB.

Circuit Voltages

• There are three main voltages that are used in the UK; the type of voltage is usually associated with an application.

Industrial - 415v

• This is often referred to as three phase and is capable of delivering the higher power requirements demanded by large industrial equipment.

Domestic - 230v

• This is the predominate voltage used in domestic dwellings

Site - 110v

• This voltage must be used on site as it is much safer that the other two voltages. Because of the unique hazards associated with site work the safest option should always be used.

Battery Operated Tools

• Battery powered tools are the safest of all power tools as the voltages are low and there are no trailing cables to cause trip hazards, or to be pulled and tangled.

415v 230v 110v

Colour – Red Colour - Blue Colour - Yellow

230 Volt Power Drill

230 Volt Power Supply / 110 Volt Transformer / 110 Volt Drill

Battery Power Drill

Electrical Hazards

• There are many hazards associated with electricity and electrical tools; we will look at some of the more common ones.

Electrocution

• This is when a person comes into contact with an electrical conductor, either directly or indirectly. Direct contact like the name suggests is when you touch a bare wire this could be due to a breakdown in the insulation e.g. old cables or a break in the in the insulation due to damage.

• Indirect contact this is when the electricity finds an alternative path through a conductive material such as a metal fence, table, equipment, etc. or a conductive liquid such as water.

• Care should be taken when using or moving conductive materials e.g. metal ladders, lengths of copper pipe, etc. around electric cables.

Fire

• One of the most common sources of fire is an electrical fault.

Trip Hazard

• Trailing leads and cables are a trip hazard.• One of the most common injuries in the

construction industry are trips and falls.• In 2012-13 an estimated 1.25 million

working days were lost through trip and fall injuries, making up half the major reported injuries that year.*

*source HSE web site.

Inspection

• Before you use any piece of electrical equipment you should inspect it to make sure it is safe to use.

• The inspection should include;– Visual inspection checking for any signs of

damage.– Damage to the lead.– PAT label is in date.

• If a tool is found to be faulty it should be reported to your supervisor.

• You should not attempt to repair the equipment as you are not qualified or authorized to do so.

• If any thing went wrong with the equipment after you had repaired it it would be your responsibility.

• If the tool is beyond repair it should be damaged in such a way that it can not be used again in accordance with PUWER 98