DC cables

[jonnyboy1]

hello lads

now im pretty new to the solar game but know what im doing, anyway after recent discussion today im wondering your thoughts on cliping both dc cables in a 2.5 twin clip together

is this acceptable or not?? one would think no for serval reasons but as the cable is double insulated its a pro to the argument.

if anyone could enlighten me on the matter it would be appreaciated

cheers

 

[GaryM]

I can't see it being a problem if they both fit the clip size correctly.
However, I'd personally prefer to see black clips for black cable, whether they're both clipped together or individually.

Or use conduit / flexible conduit.

 

[Dave-geo]

Can I ask if it is ok to run AC & DC cables in the same trunking or bundle. For instance if there is an existing ceiling track with a bundle of AC cables attached to it is it ok to add DC cable to the AC bundle?

Thanks.

 

[SolarCity]

No, you would need to keep the AC and DC cables apart.

 

[fiardor]

i try to keep AC and DC a minimum of 100mm apart.

 

[Deleted member 26818]

Is there a particular Regulation for keeping the cables separate?

 

[BruceB]

I would also like to know that. I did look some time ago and could not find one. The 'requirement' comes from a tick box on the standard PV Commissioning Test Sheet in the DTI Guide which says 'segregation of ac and dc cables' or similar.

 

[Deleted member 26818]

As far as I'm aware, BS7671 refers to segregation and separation as two separate and distinct conditions.
Separation is achieved by keeping cables a distance from whatever it is they are to be separated from, such as 50mm from service pipes etc.
Whereas segregation can be achieved by use of insulation, as long as the minimum rating of insulation of a cable is greater than the highest voltage in any of the cables, segregation is achieved.
There appears to be nothing in Section 712 of BS7671 indicating a requirement for separation.

 

[malcolmsanford]

I would also like to know that. I did look some time ago and could not find one. The 'requirement' comes from a tick box on the standard PV Commissioning Test Sheet in the DTI Guide which says 'segregation of ac and dc cables' or similar.

There is the answer ...........................the IET say one thing and the DTi as usual say something else

 

[BruceB]

I do not have a computer searchable verion of 7671, but neither separation or segregation are defined on their own and the term separation is normally used in the context of electrical separation (viz shaver socket).

Looking again at 7671 perhaps the requirement comes from 515.2. Whether physical segregation by barriers/distance is required in addition to the double insulation then becomes a matter of judgement based on perhaps lightning risks.

 

[Deleted member 26818]

I do not have a computer searchable verion of 7671, but neither separation or segregation are defined on their own and the term separation is normally used in the context of electrical separation (viz shaver socket).

Looking again at 7671 perhaps the requirement comes from 515.2. Whether physical segregation by barriers/distance is required in addition to the double insulation then becomes a matter of judgement based on perhaps lightning risks.

Yes, it is the case that BS7671 does not define either segregation, or separation.
However there are a number of Sections and Regulations that refer to both segregation and separation.
For instance Section 444.6 (segregation of circuits) refers us to Regulations 528.1-2 in order to provide segregation for cables of voltage bands I & II.
Regulation 528.1 indicates one method being: "(i) Every cable or conductor is insulated for the highest voltage present".
Following the amendment, we now have Annex A444, with Tables A444.1-2, which indicate that segregation can be achieved by means of separation.
As for Regulation 515.2, all that requires is segregation be provided, there is no indication of a preferance for a particular method of providing the segregation.
To my mind, there are a number of methods to provide segregation, separation being just one method.
Just as there are a number of methods for providing additional protection to cables concealed in walls, 30mA RCD protection being just one of them.

 

[BruceB]

Thank you for digging that lot out. I suspect you are into a level of detail beyond that which the average mcs annual audit candidate and annual audit assessor will care to get their minds around.

What they want pehaps is an answer to the question what quick, standard, simple measures can I take so I can tick that box on the commissioning sheet?

 

[malcolmsanford]

I see where your coming from here Bruce, but I'm sure you know i'm very much against these "belt & braces" approach to our industry, for IMO it is just dumbing it down .

Yes there are places for guides and to make life easy, but the DTi in my opinion are trying to create a one size fit all system, and cater for a workforce in the industry to be, for no finer point semi-skilled.

For me the package of being an Electrician is design, installation and testing, once you start to take away the training to do this, your just creating what we have now, an industry, not just PV, but the electrical one as a whole, that really is poor, producing literally "electricians" that know what to do because they have a guide that tells them, but not WHY we do

 

[BruceB]

Drifting off thread.... I agree with you, I was just reflecting what I think is the current situation. So often I read here and elsewhere people seeking proforma solutions rather than being able to understand and think through the problem they are trying to solve. Regular debates on the difference between fault/overload currents and fault/overload protection spring to mind.

 

[malcolmsanford]

Earthing and Bonding is the real classic, apart from identifying the difference between which is which and what does what, sizing it, do we need it, can we do this with it ............................you would think it was quantum physics