CS wrote:

Looking to fit a resistor/relay combination in the supply line of a
3600VA 240v isolation transformer. I reckon the resistor should be 8
ohms - based on 200% loading, but anyone know what wattage is
required???

Thanks.

Consider what happens if the relay fails to close. What is the maximum
wattage the resistor could dissipate with a short on the secondary of
the transformer? What will protect the circuit? If the protection
isn't onboard, you need to rate the resistor to stand 240V continuosly
without becoming a fire risk. That is difficult. I'd either use a much
higher value resistor and a second relay on the secondary side
controlled by spare contacts on the first relay to sequence the
application of the loads after the first relay has closed or an inline
NTC thermistor based solution (which still requires the relay to let it
cool again while the supply is on and needs adequate overcurrent
protection as well).

Google 'inrush current limiting' for some ideas.

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Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
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