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CONSUMER UNITS and DOORBELL TRANSFORMERS - separation of band 1 and band 2 circuits - BS7671
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- Опубликовано: 31 июл 2024
- Often a consumer unit will contain a doorbell transformer which operates as an 8VAC isolated supply. This means that both band 1 and band 2 voltages are present within the consumer unit. This can present a problem with the doorbell circuit wiring if standard bell wire or security cable is used.
An electrician based in Cambridge experienced this problem on a recent smart doorbell upgrade. Gary Hayers offers a few solutions for new and upgrading an existing electrical installation.
== 🕐 Time Stamps - Cut to the action 🕕 ==
00:00 Question from an electrician in Cambridge - problem with bell transformer
01:00 Band 1 and Band 2 wiring fault
01:33 Solution 1 - over-sleeving band 1 conductors
02:35 Solution 2 - wire in mains voltage cabling
03:10 Solution 3 - don't put a transformer in the same enclosure
04:30 Share your suggestions
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#efixx #doorbell #bs7671
Brilliant tip I hope Andrew now knows how to deal with this issue in the future and keeps watching these great tips from your channel
Thanks 👍
Thank you Efixx for this update, the separation of voltages has certainly become more important with the smart technology. Showing a few practical tips is always very kind. 🤩🤩🤩
3A flex would be easier than T&E.
Love Gary’s subtle sarcasm
As do team eFIXX 😯
Thanks it helped me
If the transformer is in the skip, that should be adequate separation.
I use 0.75mm2 two core flex for the secondary side.
I mount the transformer in a dedicated enclosure, and use 2core 0.75mm flex from the transformer to the doorbell. I crimp on a ring crimp at the doorbell end for ring doorbells - a nice installation.
Thank you for this video. Literally answered my question with regards to installing the transformer in the consumer unit. I don't want to see another housing on my wall to power a smart doorbell. Otherwise id fit it from my lighting circuit which would be a lot easier. Cheers
Regarding type-testing, Surge Protection Devices Ltd. say their SPD product can go into any CU because it's 'passive', i.e. not providing overcurrent or earth leakage protection. I wonder if bell transformers are largely considered in the same way?
Great comment - one to explore with the consumer unit manufacturers 👍
Excellent video guys. I ended up installing one in my cu. I used 1.0mm wire to help stop interference.
Nice one guys 👍
I have a question.ive got a 24v video door bell transformer and when i tried to install it on the load side of the circuit breaker it keep tripping and when i connected to the in side no more trip and the neutral cable i connected to the neutral bar why it trips when its connected to the load side?
Could you just have a Wylex ESE2 enclosure close to the chime with a transformer inside running off a plug to socket or a switched fuse spur ? similar to what you said run it off the light circuit thus avoiding any difficult regs?
Well....Most electrical wholesaler still lists cable as T&E, twin & Earth or 2-core and earth....so I would not get too hung up on the description, the cable manufacturers are ahead of the cable suppliers with up to date cable description. Check out your favoured Doncaster Cables decription then look at say TLC or Expert Electrical, two well known suppliers.
FCU from a socket circuit near the DB, DIN rail enclosure for the transformer. Feeding it from a spur rather than it's own dedicated circuit saves a way and when the dreaded AFDDs do come in it saves a few quid.
I also tend to wire using two core flex, the insulation has a better rating than bell wire and it's easier to fit the R clips without smashing your fingers with a hammer...
Hi iv got a friedland doorbell with built in transformer its suddenly stopped working and the bell unit is making a lound buzzing noise im not sure what that could be
Have you had any issues with that transformer as its only rates at 8VA and most smart doorbells are asking for at least 10VA
I see bell wire or cat 5 cable inside consumer units loads, my preferred method is twin & Earth to a separate enclosure for the transformer and then bell wire to the unit.
Lots to take in there, let's hope that Andrew manages to take it all in.
I was thinking of doing it this way ..I have an enclosure for the transformer so could fit it on opp internal wall
Install a door knocker. Brass ones are best. An alternative to that is a door bell that runs on POE. Run a data cable, use packets.
i tend to use 2 core flex .. but prefer to mount them externally just for the shear fact it takes up 2 ways that could be used in future
yes good point
Although it should be obvious to anyone going in the consumer unit what the cable is, not sure I'd over-sleeve it with blue ;)
I personally dislike solid core bell wire, and generally use the closest size stranded twin speaker wire. But I normally use an externally mounted transformer, and ensure adequate separation of voltage bands on new installations, unfortunately you never truly know whats going on behind the scenes in an old house though.
do you still oversleeve the speaker wire - or does it have a specified voltage rating?
@@efixx The external transformers I fit have separate compartments for the LV and ELV terminations. I've not yet found myself needing to change one mounted inside a consumer unit, But if I were to need to I will admit applying sleeving is a good solution, Thankfully most of what I do is new work and I wire a lot of heating systems so I have quite a wide variety of sleeving colours and sizes 😂
You could use 240 volt rated two core flex.
Isn't this an issue of band 2 inducing onto the band 1 cable? How about ferrite loop, and/or cross band 1 and band 2 at right angles where possible?
I sometimes wire it in flat twin double insulated flex about 0.5 mm
Excellent video thank you guys. I would just use twin and earth
Good call!
@@efixx Gary just to let you know the CPD modules I got all six so thank you. And I recommend all your viewer's have a go at them.
Is is possible to use an enclosure to install the transformer outside of the consumer unit. That way only the mains wiring for the transformer are within the consumer unit
Yes that’s another option
No power is going to my chime. Is there a fuse in the transformer that might need replaced?
Don't like the 1mm t&e, same wire different voltage? 2 core flat flex and some nicely printed label flags around it wouldn't add too much to a £200 smart bell install.
Nice. Does solid core cable have problems with DC voltage?
Not at the low current required by a doorbell
Good video but these transformers are a real throwback to the 60's. Things have moved on and 8 volts! What's that all about? Smart doorbells have different voltages so often these transformers are useless. I posted in a previous video of yours that I'm helping my son refurb his hall and he's put in wiring for a smart doorbell but as he doesn't know which one he wants we've fitted a socket in the understairs cupboard and taken the bell wire into there so a dedicated plug in psu can be plugged in.
I love Gaz
I am wondering why the doorbell circuit is usually not protected. On line side the transformer is protected with a circuit breaker, but what is going to happen in case of short circuit on low voltage side? I mean, nobody places any overcurrent protection on low voltage side when connecting the doorbell, and I'm curious why.
Is it acceptable to add another DIN rail transformer (AC/DC) next to the AC/AC bell transformer to power a low voltage DC device that needs to be located near the bell power source? I'd like to install an AC relay and small wireless device near the consumer unit that gets triggered when the bell circuit is closed (for home automation purposes).
One of the great debates of our time. I’d put the transformer and relay in with your wireless stuff rather than the Consumer unit
@@efixx thanks. Yes, it’s a tricky one as my gut instinct is to keep as much of the AC part of the setup in the consumer unit as possible, so that only the bell wire AC and DC need to come out to the relay etc. but that also puts DC in the consumer unit. Argh. If there’s no established convention, I might just throw in a meanwell 5v device I have in a spare slot and give it the ‘does it look like a bodge’ sense check.
Is that a 13a arch fault device , never seen a breaker rated at 13a before
Yep - nice 👀
To make it easier to fit the sleeving you could use heatshrink, which when shrunk has the added advantage of not easily coming off. What I did is use some of that high temperature silicone fiberglass woven yarn sleeving. The stuff I used was allegedly rated for 1200V and pushes on much easier than normal sleeving.
I have a question for you , as you have a training background, two questions actually.
Scenario...a pump house in an industrial or comercial setting, inside, two diesel engines and two electrical three phase jockey pumps, all the associated piping for the sprinklers and of course a main electrical panel controlling everything.
1. Does the panel have to have local isolation adjacent the panel, or not ?
2. What qualifications would the 'fire pump engineer' have to have to work on any part of the system, including all the voltages present within the system, from sensor voltages to 415 AC ? and I dont just mean should have, I mean HAVE not SHOULD to remain with laws,regulations etc.
-
I know this is an old video, but if gary or gordon are watching... is sleeving actually insulation? I thought it was just identification. Heatshrink is different.
3 Core 240mm warrabout dat?
Different topic ,with an led ribbon of 5metres and the driver is sat 10metres away what cable should be used and size.Asking because some lighting designers say using cat 5 cable is ok,cheers
What voltage and watts per meter is the LED tape ?
@@efixx 6watt per metre 12 volt
I give my customers a door knocker
Similar scenario is when a contactor is installed within consumer unit / distribution board and the unit is being replaced but the contactor is of a different brand
I wpuld be more worried about induced voltages where band i and bamd 2 cables run in proximity
At the currents, exposure lengths and (lack of) imbalance in a domestic situation induced voltages are insignificant.
I hope Andrew has his answer now... 👍🦾
How about 1mm T&E out from the CU to a local fused spur with a 5A quick-blow fuse fitted, and from that to the bell wire
good option
You could use spiroband wrapped round the bell wire.
I hope Andrew is now technically satisfied and removed his moustache 😆🥇👍🏻
WHo's the heavy breather @ 2 mins???
Me (Gaz) I have a medical issue (sorry)
2 CORE 0.5 or 0.75 flex maybe?
🦾
I don’t think it’s a good idea using T+E cable for a bell circuit. Reason being if it’s run under the floor it’s not obvious it’s for a bell circuit. What’s to say someone’s comes along and runs a mains cable next to it or share the same joists holes.. Incidentally when I was an apprentice in the late70s we never segregated bell wires from mains cables ,I don’t think many people did . Something we would never do now .
I assume that the higher rated insulation would prevent induced current interference. Would need a test to see though.
They don’t make bell wire like they used to
The bell wire was pathetic. Thanks for commenting 👍
POE switch & smart doorbell?
Andrew from Cambridge is no Artisan 🤣🤣🤣🤣
Could use a wireless battery door bell kit 😅
They don't so smart ones with big enough batteries yet !
2 core flex.
100% 🦾👍
Option 4 Fit a big brass door Knocker. No AFDD required
on a UVC door - someone could knock it off the hinges in a new build !
To my knowledge I don't think that would take a video
I thought there was a regulation that the transformer had to be near CU
Anorack .....
I just ask have you a wife? If they answer yes I just say “trust me they’ll let you know when someone’s at the door”