MOTOR SPACE HEATER CONTROL

[nightfox1925]

Hi Folks, I was just wondering why some of our design clients' standards sometimes specify that the motor space heater control, which is supplied from 240VAC 50Hz line to neutral supply, be connected to two (2) NC (normally closed) contactor auxiliary contacts.

In my view, since the supply is line to neutral, one (1) NC contactor auxiliary contact wired in series with the phase wire is enough. Is there any technical concerns why 2 NC are required?

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[dpc]

In the US and a few other parts of the world, both legs of a 240V circuit are hot (ungrounded). So a 240V space heater (connected at 240V) in the US would require two contacts to isolate the heater from the power source. Maybe the standards were based on US power systems?

 

[jraef]

Or they want to cover their bases with one standard practice. It isn't a problem to switch both legs in a grounded system, but it is a problem to switch only 1 leg in an ungrounded ne. So if they take the highr road, they don't need to worry about where it ends up.

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