In accordance to the National Fire Protection Association (NFPA) all electrical wiring and equipment must be in accordance with NFPA 70. Electricity is hazardous and all employees working with transformers are subject to protection. This is unless it is an existing installation which can be allowed to continue in service based on authorization of the jurisdiction in power over it.
In this article we will review basic information within NFPA 70 regarding transformers.
Transformer rooms that are made from fire-resistant construction with a minimum fire rating of an hour needs to be used with any individual, dry-type transformers of more than 112 ½ kVA rating. Below this there isn’t specific installation requirements for the room in which the transformer is located. Ones rated over thirty five hundred volts need to be installed within a vault with three hours fire-resistance.
Doorways leading into a vault from the interior of the building must have doors that are not only tight fitting but also have a minimum fire rating of three hours. One exception is when the transformers are protected by automatic sprinklers, water sprayers or carbon dioxide in which a one hour rating is sufficient.
The NFPA 70E addresses safety standards in electrical safety. These requirements are in place to protect all employees who install, maintain, and repair electrical systems and their components. It recognizes the dangers associated with electrical energy. These guidelines are in place to prevent against injury or death.
In order to comply with the NFPA 70E all employees working and operating electrical equipment above 50V must wear arc-flash protective gear. Arc-flash is an electrical current passes through the air when the insulation between electrified conductors can no longer withstand the voltage being applied. Even a flash that lasts under a second can be severe, leading to a fatality.
In order to establish compliance with the NFPA 70E there is a checklist that lays out both short-term and long-term actions to take. Some of them are listed below:
Maintenance mechanics, facility repair workers and electricians are not allowed to work on hot or live equipment while wearing all cotton apparel.
Equipment should be de-energized as much as possible before work is performed.
Hazard warning labels should be placed on all electrical equipment.
Workers should be trained in arc-flash hazards.
Logout/Tagout (LOTO) procedures need to be updated and reviewed often to be sure all control panels are included.
LOTO training needs to be constantly assessed to ensure employees are trained properly. If there is an issue they should be retrained.
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One mystery that stumps many of us is the usage of fuses in electrical components residentially and commercially. Most of the confusion surrounds the voltage, Watts, ratings and labels. Below we will look at fuses in greater detail to offer guidelines on working out the correct fuse for every situation.
What is a Fuse?
Fuses are used in electrical appliance, automobiles, homes and businesses. They are designed to prevent a flow of current that is higher than the value of the fuse. One example of this is if you choose a 3A fuse; any current flow exceeding 3A will cause a surge and the fuse will “blow”. The fuse keeps too much electricity from flowing into the equipment which would result in some type of failure such as a fire or explosion.
Any excess in current flowing through a circuit is prevented from going any further with the use of fuses. The main purpose of fuses is to prevent melting or fire from occurring under fault conditions. A fault condition is where a higher current value attempts to move through and the fuse disallows any extra current from flowing through.
The fuses value is dependent upon the power needed to allow the equipment to run properly. An appliance, such as a heater, is higher powered, requiring more current and thus larger fuses with a cable that is capable of carrying it.
Molded Main Plugs
Sometimes, as within molded main plugs, the cable is molded to the plug. The fuse is fitted within the molded plug. The fuse value is marked on the outside of the plug which makes checking the fuse very easy. In order to check out the fuse you lever it out and check to ensure the value is the same as what is marked on the plug.
Rewireable Main Plugs
Rewireable main plugs are ones in which the user can wire on their own. These plugs can handle a variety of currents and are marked to represent this. Even if a cable says it can handle a 13A fuse does not mean it should be used on your appliance. Make sure the fuse you choose matches the appliances maximum voltage not that of the cable.
Watts Verse Fuse Ratings
There is a simple calculation to determine the current amps taken by an appliance. Divide the power in watts by the mains voltage to work out the needed amps. For example, a 1900 watt divided by 230 voltages is equivalent to an 8.3 amp rating. This allows you to decide between a 3A, 5A or 13A fuse. You can obviously see that 3A and 5A will be too small for an 8.3A rating. You will need to choose a larger fuse such as a 13A.
To choose a cable with enough capacity to carry the current check the diameter of the cable. A cable of 7.5mm or more is likely to be rated for 13A or greater. Be careful to note that a 3A or 5A fuse should not be changed just because the cables rating is 13A however a 13A fuse should only be paired with a 13A cable not a lower rated cable.