Power Safety
Electricity can kill, not only from electrocution but also from starting fires. Do not exceed any ratings on equipment. If you have any doubts regarding powering your event, consult a qualified electrician.
Contents
Overloading
You should ensure that the total draw of the equipment you expect to connect is 20% less than the maximum rating for that section of your power distribution.
Overloading any section of your power distribution will result in one or more problems:
- Loss of power - circuit breakers or fuses will interrupt the supply, shutting off attendee's computers or consoles
- Melting cables, plugs or sockets - if cables, plugs or sockets are overloaded beyond their rating, they will heat up, potentially melting through their insulation
- Electric shock - if the insulation has melted exposing the metal inside the equipment, touching the uninsulated metal will give an electric shock
- Fire - if no fuses or circuit breakers interrupt the supply as above, the cable can get so hot, nearby flammable material can catch fire
Thermal Runaway
When power distribution equipment is overloaded, or run very close to its maximum rating, it can suffer from "thermal runaway", where the metal inside the equipment heats up due to the metal's resistance to the high current flow, and as the metal heats up, its resistance increases, creating a feedback loop where the metal gets hotter and hotter.
Extension Reels
Always unreel all the cable form extension reels or drums, as the reduced airflow around the tightly packed cable around the drum will heat up the cable even more, increasing the chance of thermal runaway as described above. Some extension reels have a built-in thermal magnetic breaker to reduce the risk of fire, but they can also trip when the ambient temperature gets too high, for example in direct sunlight.
Cable Thickness & Length
Thicker cable has a higher rating than thinner cable, and longer cable has a lower rating than shorter cable. This is to say that thicker cable will be rated to carry higher current than thinner cable of the same length, and longer cable will be rated to carry lower current than shorter cable of the same thickness. Always use thicker cable for high current and/or long runs, to avoid overloading the cable, and voltage drop as described below.
Electric Shock
Touching conductors carrying mains voltage will result in an electric shock, which can be fatal. During normal use, mains equipment is insulated to avoid this, but there are situations where it is possible to come into contact with mains voltage:
Damaged Plugs, Sockets or Cables
If the insulaton or casing is worn on plugs, sockets or cables, live conductors can be exposed, creating the risk of coming into contact with the conductors either directly, or through any metal items that they are touching. Remove and dispose of any items damaged in this way.
Damaged or Faulty Equipment
If equipment is faulty or has been damaged, it can increase the risk of electric shock. To ensure against this, electrical safety tests can be performed on the equipment to check if it is safe to use, using a testing device. In the United Kingdom, Republic of Ireland, Australia and New Zealand this is known as PAT Testing and in Germany it is known as DGUV Vorschrift 3.
Liquids
If liquids come into contact with electrical equipment, it can increase the risk of electric shock and also damage equipment. This can happen from drink spillages, condensation and rain. If this happens, immediately switch off the supply, remove all equipment that has come into contact with the liquid and dry thoroughly before reconnecting, to avoid further risk of shock or damage to equipment.
Voltage Drop
Long electrical cables beyond 25 to 50 meters can suffer from voltage drop, which can damage equipment. Mitigate against this by avoiding the use of long cables where possible, or using thicker cables which will have a lower resistance, reducing the voltage drop. SMPSUs deal with voltage drop very well, as they are designed to be used for any voltage between 110V and 250V. Microwaves, fridges, freezers, amplifiers and other appliances however could be damaged by a reduced voltage.
Power Surges
If there is a fault on the electrical grid causing a power surge, your equipment can be damaged. Mitigate against this with surge protectors, though it is important to understand that surge protectors have a limited lifetime, and will no longer protect against surges if they are more than a few years old.
If there is a lightning storm, unplug all equipment as no surge protector can protect equipment from lightning damage.
Protection Devices
There are several devices that protect against these dangerous conditions.
| Dangerous Condition | Protection Device |
|---|---|
| Overloading | MCB
RCBO Fuse |
| Earth Leakage | ELCB / RCD / GFCI
RCBO |
| Thermal Runaway | TMCB |
MCBs
MCBs, or miniature circuit breakers, protect against overloading, and will switch off ("trip") the power when too much is being drawn, for example if a faulty piece of equipment is short-circuiting, or too many pieces of equipment are connected. They can be switched back on once the fault or has been corrected. MCBs will have a "trip curve", usually B, C or D. An MCB with a "B" curve will trip immediately if 3 to 5 times its rated current flows through it, "C" will trip at 5 to 10 times, and "D" at 10 to 20 times. C and D curve MCBs allow for short power-draw surges and will not trip as easily as B curve MCBs when there is high Inrush Current.
Fuses
Fuses are often found inside equipment, or plugs, and in some older buildings inside the distribution board. They offer overload protection, but must be replaced when they have blown and cannot be reused, unlike MCBs.
ELCBs / RCDs / GFCIs
It is possible to automatically disconnect the supply if an electric shock is detected, by protecting ciruits with earth leakage circuit breakers (ELCBs). These devices are also known as residual current devices (RCDs), ground-fault circuit interrupters (GFCIs) or residual current breakers with over-current protection (RCBO) (see above). In some countries they are required to be installed in the distribution board with other circuit breakers, but can also be bought separately as a standalone device that is plugged in-between a wall socket and a device or extension lead.
RCBOs
RCBOs, or residual current breakers with over-current protection are the combination of a MCB and a RCD, offering both earth leakage and overcurrent protection.
