DSH 401 Mains supply transformers: Short Circuit and Overload tests
http://decisions.iecee.org/icons/ecblank.gif DSH 401
Mains supply transformers: Short Circuit and Overload tests
57.9.1
60601-1(ed.2);am1;am2
Standard(s)- (year and edition):
IEC 60601-1:1988 Ed.2 Am1+Am2
Sub clause(s): 57.9.1
Sheet n°: DSH-401
Subject: Mains supply transformers: Short Circuit and Overload tests
Key words: Over-current, protection, overload
Confirmed by CTL at its 39th meeting, in Cologne
Question:
Secondary circuit OVER-CURRENT PROTECTION is the first active component on the
secondary side of a mains supply transformer. Is the overload test performed before or after the
fuse?
Insufficient transformer winding crossover insulation and secondary circuit CREEPAGE
DISTANCES and AIR CLEARANCES causes transformer winding to short-circuit and exceed
allowable temperatures.
Decision:
If the possibility of a short-circuit exists before the secondary OVER-CURRENT PROTECTION
device (e.g. failure of basic insulation between winding or detachment of the wiring) the short
circuit test should be conducted at the exit of the wiring from the transformer.
(N.B. Similar recommendations can be made for batteries and their protective devices)
The overload test however must always be conducted after any secondary OVER-CURRENT
PROTECTION device (conform clause 57.9.1b) providing that the conditions of sub-clause
57.9.1. second dash are fulfilled.
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