Circuit Protection
Monitoring and Protection
Branch Circuits.
The old adage of putting all your eggs in one basket has never been truer when it comes to power. Mission critical servers, should not be mixed with low cost or low quality ancillary equipment such as products with a plug top power supply. With a single circuit PDU, in the event of a failure, not only the faulty item, but everything else plugged into that PDU will be brought down. A PDU that is split into branch circuits, each with its own protection, provides a secure circuit for the critical equipment and allows faults to be isolated and contained within their own secondary level branch.
Overload Protection.
Prevent unplanned power outage by specifying overload protection. Faulty equipment or failure to accurately account for the maximum possible consumption can result in excessive current draw that can pull down the entire supply to the rack. By fitting suitable overload protection to either individual or a group of sockets will limit that exposure and avoid embarrassing and costly down time. A particularly vulnerable situation is when sites suddenly switch to backup power. With a fully loaded rack, the power surges can vastly exceed the normal running load and will trip out the entire rack. Consider identifying heavy current draw equipment and protecting with individual breakers capable of withstanding short term surges.
RCD Protection.
An RCD, or residual current device, is a life-saving device which is designed to prevent you from getting a fatal electric shock if you touch something live, such as a bare wire. It can also provide some protection against electrical fires. RCDs offer a level of personal protection that ordinary fuses and circuit-breakers cannot provide.
RCBO Protection.
An RCBO is a type of circuit breaker with two functions.
- 1. To protect life
- 2. To protect an overload on a circuit – overcurrent and short circuit
An RCBO (Residual Current Breaker with Overcurrent) is used where there is a need to prevent overload on a particular circuit at the same time as preventing anyone getting a shock that has the potential to kill them.
MCB Protection.
MCBs or miniature circuit breaker are electromechanical devices which protect an electrical circuit from an overcurrent. They work by the principal of overload versus time, a small overload is tolerated for a greater length of time than a large overload. This takes into account short term switch on surge. An MCB will protect cables from overheating and catching fire.
How to correctly size kA ratings of circuit breakers
One of the most important safety aspects to consider when designing an electrical circuit is to correctly size the circuit breaker fault current rating (commonly called the kA rating).
So what is the kA rating?
The value of the kA rating determines how much current the circuit breaker can withstand under fault conditions.
The circuit breaker only has to withstand this for a brief period of time, usually the time it takes for the circuit breaker to
trip.
For example, a value of 6kA means that the circuit breaker can withstand 6,000 amps of current during the brief time it
takes to trip.
Why is the kA rating so important?
Under fault conditions such as a short circuit, much more current flows through the circuit than it was designed for.
A circuit that was designed for a maximum of 20A may suddenly be drawing hundreds, if not thousands of amps.
The circuit breaker will trip if this occurs. However, what if during a short circuit there is more current flowing through the circuit than the kA rating of the circuit breaker? In this case the circuit breaker will fail.
One possibility is that the contacts in the circuit breaker will weld, thus preventing the circuit breaker from tripping, resulting in damage to the cable, or in extreme cases a fire.
Another possibility is that the circuit breaker explodes, as a result of the copper in the circuit breaker overheating and turning into dangerous plasma. This could be very dangerous to people nearby, for example the electrician turning the circuit breaker on after a fault.