Contact voltage calculations for LV electrical methods

There are two primary strategies of safety towards electrical shock, the primary being termed primary safety which is safety towards direct contact of individuals or livestock with stay electrical components. The second methodology of safety is fault safety which is the safety of individuals or livestock towards contact with uncovered conductive components which had been made stay throughout a fault situation.

The contact voltage idea, which is a quite simple however vital security idea, is worried with the latter methodology. The definition of “contact voltages” is these voltages that exist between concurrently accessible uncovered and extraneous conductive components which will result in the danger of electrical shock within the occasion of {an electrical} fault.

The American Normal NFPA 70E defines “contact potential” as a floor potential gradient distinction that may trigger present circulation from hand at hand, hand to foot, or one other path, aside from foot to foot, by the physique. The British Normal BS 7671 doesn’t explicitly check with “contact voltage” however refers to safety towards electrical shock.

!    Observe that simply because a chunk {of electrical} tools is correctly earthed that it isn’t doable to obtain an electrical shock throughout a fault. That is fully incorrect.

In a appropriately designed electrical set up all uncovered conductive components which can be touched, both instantly or not directly, have to be earthed and bonded again to a standard earthing level similar to the principle earth bar. Throughout an earth fault, a contact voltage is developed resulting in a danger of shock which isn’t eradicated by earthing or bonding. It’s the goal of {the electrical} safety methods throughout such an earth fault to make sure the fault is disconnected quick sufficient to make sure the contact voltage created is not going to be dangerous to any individual or livestock which is uncovered.

Bear in mind the danger of hurt to an individual from publicity to the touch voltages will depend on each the voltage magnitude and the period of publicity (fault clearing time).

Lp-curve is for moist situations.


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