Couple of questions about plug-in relays

[JohnW2]

With respect to the ubiquitous 'industry standard' 8-pin (and 11-pin) round-based plug-in relays, when used within a domestic electrical installation:

1...Does the entire relay have to be enclosed, or is it acceptable for the top of the cover of the relay to protrude through an opening in the enclosure? On the face of it, the cover would seem to provide perfectly adequate insulation.

2...Is it OK to mount them horizontally, rather than the more usual/ obvious vertical? I've looked at the data sheets of many makes, all of which are surprisingly silent on this question. In terms of function, there clearly would be no problem in the energised state. The only possible problem I can think of is that one could end up with gravity working against the spring which returns the armature and contacts to the 'off' postion when the coil is de-energised, which could conecivably cause problems if the spring grew weak. However, if one mounted it with pins 1 & 8 (standard connections) uppermost (i.e. coil uppermost), gravity would actually be aiding the return to the 'off state' - so presumably no problem? I have to say that I've often done this, and have never been aware of any problem.

Situations (1) and (2) above would obviously both arise if one used a DIN enclosure like those intended for RCDs etc. (with appropriate blanking) to house the relay.

Kind Regards, John

 

[Stoday]

Oh nostalgia

The 8-pin base was the same as the International Octal valve base that became obsolete in the 1950's. Valves moved on to better bases but relays remained. Miniture valves were superceded by semiconductors but some relays remained stuck in the 1950's.

I know there was an attempt to build a computer with relays. I guess they are still trying to flog off the stock of relays that became obsolete when the relay computer was scrapped.

 

[jj4091]

I think the answer to both your questions is yes, it is perfectly acceptable to use them in the ways you require. In fact the cover protruding through something will act as a support when mounted horizontally.

 

[bernardgreen]

Any position is OK on static equipment ( normal gravity ) with the provisor that retaining clips should be used if the relay is not vertical with pins at the bottom.

That said there are a few special relays using octal and 11 pin bases that must be mounted vertical. Mercury wetted and high sensitivity types for example but these will be un-likely in domestic situations.

The cover over the terminals of the base is normally accepted in industry as fully compliant with safety requirements. Enclosing the relay might lead to overheating of the coil.

 

[ban-all-sheds]

I know there was an attempt to build a computer with relays. I guess they are still trying to flog off the stock of relays that became obsolete when the relay computer was scrapped.

http://web.cecs.pdx.edu/~harry/Relay/

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[Taylortwocities]

Ahh, that takes me back to the old strowger days.



The answer that the computer gives will always be
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42

a number that looks even better when shown as a binary display on those lights. Work it out and you'll see why............

 

[JohnW2]

Oh nostalgia
The 8-pin base was the same as the International Octal valve base that became obsolete in the 1950's.

Speak for yourself (about 'obsolete') I still have some things (still working when last tested) using octal-based valves - although, admittedly, most of what I've got uses 'minature' valves with B9A or B7G bases.

I know there was an attempt to build a computer with relays.

Indeed, and not just 'attempts' - and even those based primarily on thermionic valves also contained vast numbers of relays. ... and that's not to mention the vast amount of electromechanical stuff which was in telephone exchanges - up to the '60s, at least, until 'System X' was phased in. As a leftover from that, I think that the PSN still supports oule dialling to this day.

I guess they are still trying to flog off the stock of relays that became obsolete when the relay computer was scrapped.

Although relays have largely gone from electronics, except as a means of output control (and, even then solid-state alternatives are often used), I would still say that relays (and 'contactors', if there's a difference!) still have a very valuable place in 'electrical' situations. Solid state relays and switches just do not afford the comfort/safety of mechanical disconnection.

Kind Regards, John

 

[JohnW2]

I think the answer to both your questions is yes, it is perfectly acceptable to use them in the ways you require. In fact the cover protruding through something will act as a support when mounted horizontally.

Many thanks. That's obvioulsy what I was hoping to hear.

Kind Regards, John.

 

[JohnW2]

Any position is OK on static equipment ( normal gravity ) with the provisor that retaining clips should be used if the relay is not vertical with pins at the bottom.

Thanks for confirming.

That said there are a few special relays using octal and 11 pin bases that must be mounted vertical. Mercury wetted and high sensitivity types for example but these will be un-likely in domestic situations.

Agreed, but I'm only concerned with bog-standard relays.

The cover over the terminals of the base is normally accepted in industry as fully compliant with safety requirements. Enclosing the relay might lead to overheating of the coil.

I'm not sure that I understand what you mean by 'the cover over the terminals of the base'. Most, perhaps all, octal and 11-pin relay sockets I know of have totally exposed terminals. Are you perhaps just saying that, as I was suggesting, an enclosure which denies access to those terminals (but which leaves some of the relay cover exposed) is adequate?

Kind Regards, John.

 

[bernardgreen]

The covers are ( were ) a shroud which fits over the base with a clearance hole for circle of pins on the relay. Some clip onto the relay base and some depend on the relay to hold them in place.

I haven't seen them used for a while now but for bench lash ups they were ideal for covering the bases with terminals where the wire wrapped round a large screw terminal.

 

[JohnW2]

The covers are ( were ) a shroud which fits over the base with a clearance hole for circle of pins on the relay. Some clip onto the relay base and some depend on the relay to hold them in place.
I haven't seen them used for a while now but for bench lash ups they were ideal for covering the bases with terminals where the wire wrapped round a large screw terminal.

I must confess that I had a vague recollection of such things, and also of 'skirts' which extended a little way up the relay, to prevent pins being exposed if they weren't fully plugged in, but I recently had a pretty good search and could find no evidence that either are any longer available. Does anyone know of anything like this which is available?

As an aside, the 'watch this thread' facility of this forum doesn't seem to be working for me to day - I'm not getting e-mail notifications that messages have been posted in threads I'm 'watching' - is this just me?

Kind Regards, John

 

[ericmark]

What you have to consider is the IP2X or IPXXB. or IP4X or IPXXD as appropriate. From the top you must not be able to put a 1mm rod through any hole that will connect to live terminals. From the side it's the British standard finger 12 mm with knuckles can't remember exact dimensions.

In real terms some common sense. Where there are children then maybe we should be looking at less than 12 mm. Also any barrier needs to have a tool or key to be removed. This in practice is often not the case with push-on covers used on consumer units where MCB's don't fill the hole. Again common sense means you look at where it is mounted unlikely adults will try to remove the blanks with their fingers but children are good at fiddling with any blanks hence why those silly blanks that are put into 13A sockets are so bad. Children love to play with them.

Abroad the relays are often found in hotel consumer units and switch on the AC once you have paid the surcharge. They are also often fiddled with many having bits of card inserted to force contacts in so the customer does not need to pay for using the AC.

With this in mind I would use a box with lid so know one knows what is inside so less likely to remove a lid needing a screw driver to see what they do than noting what works once the fee is paid.

 

[JohnW2]

What you have to consider is the IP2X or IPXXB. or IP4X or IPXXD as appropriate. From the top you must not be able to put a 1mm rod through any hole that will connect to live terminals. From the side it's the British standard finger 12 mm with knuckles can't remember exact dimensions.

Yes, I realise that, but it's not a significant issue with what I was talking about - since, with horizontal relay mounting, all potential openings are on the front, not top, and achieving IP2X or IPXXB is no problem. If one does, as I mentioned, use an 'RCD enclosure' (or even a small CU enclosure, for multiple relays), gaps at the side of the relay(s) (if they arise - most of these relays are almost exactly '2 modules' in width) can be dealt with, but with most relays there is about a 5mm gap above and below the relay. Whilst that easily satisfies IP2X/IPXXB, I would not be happy with that situation (the screw terminals of the relay base are directly below those gaps), and would do something to more-or-less elimate the gaps.

I've always been a little surprised by the different requirement for the top surface of an enclosure (or, to put it another way, the fairly modest minimum IP requirement for everything else). I presume that it exists because of the possibility of things 'falling in' from above, but it is often the case that it is the least accessible surface (although I realise that 416.2.2 does not actually require IP4X / IPXXD for the top surface if it is not 'readily accessible') - and, more importantly, the sort of people (notably children) who are inclined to stick metallic objects into gaps are probably most likely to probe gaps on front surfaces. I certainly would not want a 10mm diameter hole, with live parts below, in the front surface of an enclosure under any circumstances, and certainly not if there were, or could be, 'little people' around!

Kind Regards, John.

 

[ricicle]

I was still using octal relays in our factory panels up until about 5 years ago when most of the machines were refurbed and the modern square relays looked better in the new panels

 

[JohnW2]

I was still using octal relays in our factory panels up until about 5 years ago when most of the machines were refurbed and the modern square relays looked better in the new panels

That doesn't surprise me at all. Aesthetics is obviously an individual matter - but, in terms of functionality, as far as I am concerned, octal-based relays are not broken, so don't need mending (or replacing). I try not to think about how long ago it must have been when I first used one, or how many I have used over the decades - and I can't actually recall a primary failure of one of them during 'normal' use !

Kind Regards, John.