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I am in dilemma if I can use a relay(SPDT) with contact rating of 250VAC and 16A to switch 1000VAC and 2A? The switching power is still lesser than the maximum switching power. But I am worried that the high voltage might have adverse effect on relay. Your help will be much appreciated. Thanks.


marked as duplicate by The Photon, DoxyLover, Wesley Lee, Dmitry Grigoryev, laptop2d Mar 30 '17 at 15:19

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    \$\begingroup\$ What doe the max voltage say on the relay spec? \$\endgroup\$ – Trevor_G Mar 29 '17 at 21:46
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    \$\begingroup\$ "Switching power" is a meaningless concept. The maximum voltage and maximum current ratings of a switch or relay are independent of each other, and BOTH must be obeyed at all times. \$\endgroup\$ – Dave Tweed Mar 29 '17 at 21:52
  • \$\begingroup\$ The data sheet says max. switching voltage is 440VAC. \$\endgroup\$ – gsubas Mar 29 '17 at 22:26

No, and especially not if you plan to use this in a product. There are several reasons for this: The contacts will arc and the relay will not shut off when open. There are creepage and clearance distances, going over the rating will make it impossible to clear regulatory. Another problem involves the contacts, they are designed to maintain a certain contact resistance, if the voltage is exceeded you could get welding to the contacts at worst case or a degradation of the contacts.

If this is just for a hobbyist\prototyping application, your welcome to try it YMMV and your relay could go up in smoke as well as burn up your input.

  • \$\begingroup\$ It depends if the rating is a sales rating or a spec rating though... Reading the specs may show you safe operating graphs or other tables or values that are different from the sticker on the side of the box. I very much doubt it will go up to 1KV though... \$\endgroup\$ – Trevor_G Mar 29 '17 at 21:51
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    \$\begingroup\$ Thats why I say "You could try it" but you don't know how big the gaps are. On some of the relays I've used they still have some arcing at 220V for a very short while after you open it. I know the gaps are quite small, I'm willing to bet 1000V AC will have no trouble bridging the air gap on most relays. You might be able to push it to 300V or 400V but my intuition tells me that 1000V is way too much \$\endgroup\$ – laptop2d Mar 29 '17 at 21:53
  • \$\begingroup\$ Yes, exactly... \$\endgroup\$ – Trevor_G Mar 29 '17 at 21:55
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    \$\begingroup\$ Another thing to think about is the contacts... they'd get more wear and tear or other bad things could happen \$\endgroup\$ – laptop2d Mar 29 '17 at 21:57

I wouldn't recommend using this relay as you propose.

Even though contact ratings are expressed in volts and amps, they are not to be considered as an overall "power rating" as you suggest. Therefore, you cannot trade off voltage for current as you would in certain other devices (e.g. a power transformer).

The reason is that the voltage rating of a pair of contacts is determined by one set of parameters, while their current rating is determined by another set of parameters.

The voltage rating is primarily set by the distance between the contact's actual contacting surfaces while the contacts are in the fully open position. This distance prevents the applied voltage from directly arcing thru the air space between them. Further, the conductive members which carry the voltage to the contacts must also be kept a safe distance apart throughout their paths within the relay structure, and from the relay's coil windings & coil terminals in order to prevent arcing between these various elements, which may or may not be fully or partially insulated.

On the other hand the current rating of the contacts is determined by the diameter and thickness of the contacts and their conducting members. A larger current rating requires larger diameter and thicker contacts. The metal the contacting surfaces are made of is also important. Some materials are superior for certain ranges of currents than others. The shape of the contact matters too. This minimizes arcing when an inductive load is switched. Contact materials are often different for AC & DC loads, as well as for the range of expected load and switching currents.

Choose your relay carefully and conservatively and it will provide long and reliable service.


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