Dry Contact and Hermetically Sealed Switches


Thread Starter


I'm trying to understand the need for a dry contact switch or a hermetically sealed swtich. Most literature that I've read points to a recommendation to use hermetically sealed switches for corrosion resistance.

I'm trying to understand the recommendation in today's applications for hermetically sealed switches. If a dry contact switch is purchased and is to be installed inside of a aluminum housing assembly which is IP 66 (Nema 4X) and explosion proof, I can't see the full need for specifying hermetically sealed switches.

However vendors still offer options to purchase a hermetically sealed switch that will be located inside of an IP 66 explosion proof enclosure and still recommend hermetic switches for specific applications.

I haven't been able to find specific literature to differentiate the need, however, I think that a hermetically sealed switch would be beneficial when the switches are not located inside of an enclosure which offers hazardous area certification and ingress protection.

Is it such that even if installed in these enclosures humidity or corrosion could still form inside of the enclosure?

Thanks in advance for any information.
No question that environmental protection is a major reason for hermetic sealing in general purpose switches.

But hermetically sealed switches are used in Class 1, Div 2 (zone 2) because the hermetic sealing seals in any microswitch contact arcing/sparking is used to qualify for the 'non-incendive' rating.

I don't think hermetic sealing is a acceptable as means of protection in Class 1 Div 1 EXP, but it is for Intrinsic Safety. I suspect Cl 1, Div 1 EXP hermetic sealing is just a 'better switch' for a high end product. One of the industrial pressure switch vendors could probably clarify for you.
First of all NEMA 4 X is not explosion proof, you need NEMA 7 for that.
IP 66 refers to the Ingress Protection, similar to NEMA 4.

A dry contact refers to any contact not connected to a source of power such as the contacts of a relay or the button for a doorbell.
A solid state output like an SCR or Triac would not be a dry contact.

Hazardous areas are little understood, often you see the installation has gone overboard with great explosion proof boxes where really they weren't required at all by code.

For example an old open frame 3 phase motor can meet Class 1 Div 2.