Discussion From WANTED: A Cable Box

[pistonbroke]

Originally Posted by cupid stunt

We have differed from the subject slightly !

Equipotential bonding is only carried out to water & gas services at point of entry to the property

Main Equipotential Bonding to water & gas services at point of entry to the property within 600mm and before any branch, also only required if those services and any other services are metallic and that are in the Terra-Firma, including metal stack pipes.

I think he meant Supplementary Equipotential Bonding.

Regards

[Rick]

Look at an apartment block. You have say 100 flats. 1/3 of those are on one phase, the 2nd 1/3 on another and so on.

ALL 100 flats can be provided Terrestrial, FM, DAB, Satellite, Cable from one source. i.e. One Dish. Or one Antenna. This is called an IRS system. Now go look in a service riser, you'll find multi switches, launch amps and all sorts of other gubbins ALL EARTH BONDED

You have the potential in that scenario for any of the three phases to come into contact with each other through it, given fault conditions at one or more STB's. Hence why the system must be correctly earth bonded. The fact that the STB's themselves are double insulated, so don't require an earth themselves it totally irrelevant to the scenario being discussed.

As for

By merging the 2 selv from 2 independent sources, indeed 2 phases you have breached that reg.

the regs haven't been breached by merging the two systems. The regs have been broken because the merged system has not been correctly protected.

When cs measured 15v DC at the LNB, he is measuring that derived from a single phase, 240v. 2 or more phases don't become involved under normal operating conditions. So I don't know where you get 25.98v from ?

[cupid stunt]

Originally Posted by pistonbroke

@cupid stunt,
I dont know how you got 15v dc at the lnb ?

15V dc or there abouts is the voltage to the LNB ??!?!

Firstly its not pure dc it is derived from 230v transformed ac to rectified 15v dc

And ?

Theoretically it will be 25.98 v dc from any two phase angles based on 15v.
Remember 2 separate phases.
How this affects the lnb and sat system I do not know its not my area of knowledge, you will have to see what the voltage rating of it and the associated equipment is, also because it has come from 2 phases I would imagine it has a lot of harmonics in the circuit not a good idea really even if it is filtered.


Also from your avatar I see your a sparks !!
You should then be aware that under iee regs it is required to have physical separation of the live parts of selv and parts of wiring systems and circuits (414.4.2). By merging the 2 selv from 2 independent sources, indeed 2 phases you have breached that reg.
Regards

Yes I am aware of the regs this was a temp setup while scaffolding was up (2weeks) I checked for 30mA RCD protection in both properties before connecting. therefore, any leakage to ground or back through another phase will disconect the RCD.
Regards.

C.S.

[cupid stunt]

Originally Posted by pistonbroke

I think he meant Supplementary Equipotential Bonding.

Regards

Supplementary bonding is only local to pipes and metallic objects, like cable tray, heating pipes etc, and should not be taken out of the equipotential zone. the 17th ed has also relaxed the regs on supp bonding due to whole 30mA RCD protecion.

[Rick]

Originally Posted by cupid stunt

this was a temp setup while scaffolding was up

If you have to do it again m8, i'd suggest using a bonding bar on each side, or if you can weather proof it, by the dish. Get it earthed out. As much as anything, your backs covered if anything does go wrong

[cupid stunt]

Cheers Rick.

Much appreciated

[pistonbroke]

@ Rick,
Firstly apologies but when I first viewed this thread and going to reply there was no reference to a IRS system.

The only reference was 2 houses next to each other there was no mention of a commercial situation (flats) that only appeared after I posted so my references were to that post, not sure what happened I think I was in the other thread at the time sorry.


But any how your post #22
I could not agree with you more with the IRS system, my only surprise is the designers of such premises would overlook the 400v scenario in the “Landlords” part of the building especially as the equipment is low powered and negligible benefit across 3 phases.


“the regs haven't been breached by merging the two systems. The regs have been broken because the merged system has not been correctly protected”.


As I said we were talking 2 different scenarios and agree with the bonding scenario.


But afraid to say the regs have been breached by merging 2 or more systems which have been derived from separate sources. But if the lnb's are isolated then perhaps not and forgive my ignorance if they are isolated.
Rick if you have a regs book please read reg #414.4 particularly #414.4.2 (v) it states “Physical Separation” as a requirement in the regs. We are not talking earthing/bonding here but “live” conductors.


“When cs measured 15v DC at the LNB, he is measuring that derived from a single phase, 240v. 2 or more phases don't become involved under normal operating conditions. So I don't know where you get 25.98v from” ?


Maybe I miss interpreted what was said ?


I understood that he joined another coax to the lnb which already had a coax attached ? Does that not common the 15v core on the lnb therefore merging the 2 systems from 2 separate phases? Or are the lnb's isolated if so again forgive my ignorance.
As for the measurements where did he measure ? core – core or core – braided shield ?


Regards

[pistonbroke]

@cupidstunt
Its good to have banter as these regs of ours have always been open for interpretation the 14th was basic, the 15th was a nightmare, the 16th was better and the 17th better again. It is still flawed but they cant introduce too much at once.


“Yes I am aware of the regs this was a temp setup while scaffolding was up (2weeks) I checked for 30mA RCD protection in both properties before connecting. therefore, any leakage to ground or back through another phase will disconect the RCD”.


As I said before I not sure what type transformer the STB has I assumed double wound, if it is then the RCCD would not come in to play. It would not be able to detect a fault on the secondary windings as they are physically separated, it will only monitor the primary windings/circuits.
The equipotential zone is another abnormality, its not spoke of much in the 17th regard area covered but some people see the zone as inside the property only. In fact metal fire escape staircases bolted directly to the ground require a main bond not supp bonding. Then there is a new building within the boundary but separate to the original but from the 230v same source but as a sub main.



Certainly the 17th has alleviated most needs of supp bonding but not all where an RCCD is employed, but an RCCD is not always required when other criteria has been met e.g surface installation/metallic sheath. Then supp bonding may be required.


If you would like to continue on this i would suggest we speak elsewhere as this it really relevant to the thread.



Regards

[Rick]

Under normal operating conditions the LNB's are independant from each other, a quad operates as four single LNB's. So under normal operating conditions there is absolutely no interaction between equipment on differant phases. It's only under fault conditions that that becomes a possibility. Hence the bonding required.

The 15v would have come from measuring the inner di-electric accross the outer braid, Whilst connected to the reciever. Had a horizontaly polarised channel been selected on the reciever, the measurment would have been around 18v

I split the thread before because it had gone off topic, I will split it again and move it to the DIY section later

[cupid stunt]

STB's dont use centre tapped wound transformers or double as you call them, you will only find them in shaver points or 12V bathroom fan units.etc

If there was an unequal potential of 230v between STB's connected to the LNB the RCD would opperate accordingly.

I had a customer with a VHS video machine recently that went faulty and produced 90V through the RF out, causing the RCD to opperate.

VHS = Video Home System for those who forgot

Regards,
C.S.