12V Bell supply & mains relay in one enclosure: Does it comply?

[Mark42]

A 24Vdc door bell supply, provided by a transformer and relay near the main DB. Various bell-pushes and 24V bells around the site. All in mains-rated cable and often run together with mains looms.

The original bell in my workshop was not audible when machinery is running.

Single bell replaced this evening with a 24Vdc n/o relay, with mains supplied from a dedicated 2A MCB on a local Hager sub-main. No RCBO on this circuit. All cables clipped direct (and visible) in loft space.

The single-pole relay output powers a mains bell, and a 500W mains halogen light to give visible confirmation of the door bell. (I’m not sure how long the lamp will last with all that flashing from cold though.)

All the gubbins (note technical term) is in a Wiska IP66 box. Please ignore the untidy placement of the accessories: this is due to obstructions and cables behind the panel. The bell above the light is a telephone ringer, not related to the other electrical items.

A major re-wire at my house is nearly finished, and due for inspection and certification soon. This is the sort of ‘interesting’ detail which might be scrutinized. Not sure about the separation of LV and ELV in the same enclosure. Does it comply?

Thanks, Mark.

 

[telectrix]

perfectly acceptable. dozens of cases where a relay with a 12v coil switches 230v. 1 suggestion regarding your concern about the halogen flood. you could replace with a 12v strobe light, available from any alarm supplier.

 

[Mark42]

Thanks Telectrix for the super-quick reply! You’ve put my mind at rest.

The strobe is a good idea, but my reservations were as follows:

1. I’m not sure how long an alarm strobe takes to charge its condenser and output its first flash. A short press on the door bell might not be enough.

2. I want to load the 24V bell transformer as little as possible. I use mainly 24V fire alarm bells as doorbells, since they are very low current (having a small motor and a rather mickey-mouse rotating cam, rather than a solenoid striker.) Some of them are run via a couple of cores of the 25-pr CAT 5 which connects all my buildings together (future-proofing: I want to dig trenches only once!) They still work at the end of 150m of 0.5mm.

3. Strobes of any kind (even slow ones) where there is rotating machinery feels wrong. I read somewhere about workshops needing fluorescent lighting on more than one phase to prevent dangerous stroboscopic optical illusions in rotating machines. I’ve no idea if it’s rubbish or not.

I’ll see how well the lamp lasts. Alternatively, I though about interrupting the supply to one of the twin fluorescent ceiling lights, since they are nearly always on when the building is in use. A 24V n/c relay could be secured inside the fitting.

I work from home on a sprawling rural site, and can never be found. The door bell is used by my girlfriend to call me in when a cup of tea, or lunch, is ready (three rings means feeding time: it’s all very Pavlovian.) Clearly it is very important that I don’t miss these calls, so I’m full of these weird electrical ideas …

 

[Darkwood]

Most control panels have multiple voltages in but the only comment i will make is to tag the cables with number collars L/V and SELV i.e. 24 and 230 respectively, plus mark the lid up with with a note of 2 voltages and require isolation from 2 seperate sources (assuming you have put transformer and bell/light on different circuits). The ideal setup here would be 1 supply into adaptable box with fusing down four your bell, transformer and light within box and this way mcb will isolate all within which can be dist' board and fuse i.d. on lid. There is always the path of confusion if someone isolated transformer followed into box and didnt realise 230v still existing in there from other sources.

 

[Darkwood]

Thanks Telectrix for the super-quick reply! You’ve put my mind at rest.

The strobe is a good idea, but my reservations were as follows:

1. I’m not sure how long an alarm strobe takes to charge its condenser and output its first flash. A short press on the door bell might not be enough.

2. I want to load the 24V bell transformer as little as possible. I use mainly 24V fire alarm bells as doorbells, since they are very low current (having a small motor and a rather mickey-mouse rotating cam, rather than a solenoid striker.) Some of them are run via a couple of cores of the 25-pr CAT 5 which connects all my buildings together (future-proofing: I want to dig trenches only once!) They still work at the end of 150m of 0.5mm.

3. Strobes of any kind (even slow ones) where there is rotating machinery feels wrong. I read somewhere about workshops needing fluorescent lighting on more than one phase to prevent dangerous stroboscopic optical illusions in rotating machines. I’ve no idea if it’s rubbish or not.

I’ll see how well the lamp lasts. Alternatively, I though about interrupting the supply to one of the twin fluorescent ceiling lights, since they are nearly always on when the building is in use. A 24V n/c relay could be secured inside the fitting.

Note #2 .. your best bet would be a klaxon sounder as they will be heard above most natural factory environments, make sure your doorbell sounds do not immitate the fire alarm as been the same tone/noise.

Note #3 .. strobes are fine as low frequency flashing and the stroboscopic effect will be present only if lighting over 1phase and inductive type lighting (e.g. switch start flourescents as these flicker at about 100hz), high frequency fittings wouldnt have this issue, a small modular timer would ring bells and strobe for any duration you set if fitted.

and last suggestion of a relay in fitting that breaks switch wire well... just drop that idea in the bin, not a good idea for many reasons.

 

[Mark42]

Note #2 .. your best bet would be a klaxon sounder as they will be heard above most natural factory environments …

… a small modular timer would ring bells and strobe for any duration you set if fitted.

Yes, I had originally thought about using an EZ003 in the Hager DB, and a strobe. (I used one for a spark igniter in a gas fire bowl over a pond in another project – the propane gas solenoid stays on with the switch, but the EZ003 stops the sparker after 5s – A useful piece of kit, but expensive.)

But using one here would prevent the system being used for multiple signalling at my home – most visitors press the doorbell only once or twice, three rings means the girlfriend has tea ready, and so on. (And ten rings means stop butchering wood in your bloody workshop and come to bed NOW!)

It’s more than just a simple doorbell.

…make sure your doorbell sounds do not imitate the fire alarm as been the same tone/noise.

Yes, very good point. The fire alarm will be electronic whoop-whoop sounders. These are good because you can fit additional standard plates in bedrooms, fed down two cores of the CAT 5 which also carries the telephone. Non-compliant but this is not a commercial installation.

Note #3 .. strobes are fine as low frequency flashing and the stroboscopic effect will be present only if lighting over 1phase and inductive type lighting (e.g. switch start fluorescents as these flicker at about 100hz), high frequency fittings wouldn’t have this issue,

Ah, thanks for the explanation. I’m gradually changing to HF everywhere anyway.

and last suggestion of a relay in fitting that breaks switch wire well... just drop that idea in the bin, not a good idea for many reasons.

Yeah, just a thought experiment really. Agreed.

Most control panels have multiple voltages in but the only comment i will make is to tag the cables with number collars L/V and SELV i.e. 24 and 230 respectively, plus mark the lid up with with a note of 2 voltages and require isolation from 2 seperate sources (assuming you have put transformer and bell/light on different circuits). The ideal setup here would be 1 supply into adaptable box with fusing down four your bell, transformer and light within box and this way mcb will isolate all within which can be dist' board and fuse i.d. on lid. There is always the path of confusion if someone isolated transformer followed into box and didn’t realise 230v still existing in there from other sources.

All excellent points, Darkwood, thanks.

It’s certainly a good idea to put the whole thing in a single box with a single supply as you suggest.

I didn’t know it was necessary to provide a ‘Warning: This installation has two supplies’ notice when one of the supplies is ‘only’ SELV. Thanks for that, I’d missed it.

The difficulty here is that it’s an extensive system, but with one 24Vdc and one 12Vdc supply for everything. They are in my main equipment box pictured below. This also provides DC for all manner of other control kit – relays for external lighting, relays for central heating TWAs on all the radiators and an AMX home automation system, currently in progress. I didn’t want to have a shed-load of separate (hot) transformers all over the place, in forgotten corners of the wooden building.

Thanks for the advice and comments. I work alone here in my own little world, so outside opinion is always welcomed!

I do worry that when the inspector-dude from the Local Authority turns up to ‘test’ my DIY domestic installation, he is going to think, “What the **** is all this?” and run, foaming at the mouth, away …

 

[Darkwood]

cat 5 your doorbell to a modular phone dialer with multi channel response so as to send you a txt message depending how many presses of the doorbell will send different message. A logic controller can establish the no' of presses and any delays before sending the signal to correct channel on auto dialer. This way you get a buzzing phone and txt .... yes crazy over the top but seems you've gone down that road already:wacko:

 

[Mark42]

cat 5 your doorbell to a modular phone dialer with multi channel response so as to send you a txt message depending how many presses of the doorbell will send different message. A logic controller can establish the no' of presses and any delays before sending the signal to correct channel on auto dialer. This way you get a buzzing phone and txt .... yes crazy over the top but seems you've gone down that road already:wacko:

Thanks, Darkwood, for your thoughtful suggestions, all eminently useful and not at all over-engineered!

But there’s a fatal flaw: this is rural Norfolk and mobile phones don’t work.

That’s exactly why I put bells everywhere in the first place

 

[ringer]

I realise this is your own property and not a commercial premises, but you really should not have wooden doors and door frames enclosing distribution boards and control panels. Big fire risk. I hope you have a robust smoke detection system in place.

Sent from my HTC Sensation using Tapatalk

 

[Mark42]

I realise this is your own property and not a commercial premises, but you really should not have wooden doors and door frames enclosing distribution boards and control panels. Big fire risk. I hope you have a robust smoke detection system in place.

Hi Ringer, yes, I guess you’re right, but what’s the alternative? What do other people use in their homes? I’ve never seen steel doors in someone’s house!

Plus I bought 2 cu m of lovely oak on EBay and am using it everywhere in my refurb.

No, there are no smoke detectors – it’s too close to my kitchen where I like to occasionally make crispy bacon. But there are heat detectors. The fire alarm system is in progress – the third box up on the left hand side.

This will signal direct to the emergency services via a monitoring company I already use for the intruder alarm (I store high-risk goods so the Police insist on this). That’s why I’ll only use heat detectors (a mix of fixed temp and rate-of-rise types) because I don’t want firemen turning up every time I have a bacon sandwich.

Primarily because they’ll all want one too

 

[Darkwood]

Thanks, Darkwood, for your thoughtful suggestions, all eminently useful and not at all over-engineered!

But there’s a fatal flaw: this is rural Norfolk and mobile phones don’t work.

That’s exactly why I put bells everywhere in the first place

walkie talkies then ... the old mans mobile short range phone

 

[Darkwood]

Thanks, Darkwood, for your thoughtful suggestions, all eminently useful and not at all over-engineered!

But there’s a fatal flaw: this is rural Norfolk and mobile phones don’t work.

That’s exactly why I put bells everywhere in the first place

walkie talkies then ... the old mans mobile short range phone