Electrical Design Query
A few weeks into my phase 3 attachment and I am working on the design of the M&E install for the onshore facilities of an EDF wind farm in Scotland. EDF are the client with Skanska as the principal contractor. My design consultancy have been employed by Skanska to design the M&E. Unfortunately, General Electric and National Grid are also involved and have employed an independent consultant to review the electrical design. One recommendation that he has made is that all final circuits need to be terminated into a junction box in each room. The junction box is then to be connected to the distribution board via multi-core armoured cable. He believes that this will save time on the install and is more cost effective. I am recommending a standard install to and from the distribution boards and am struggling to see the benefits of employing his method.
Any thoughts from the M&E crew on this?
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What is the makeup/layout/size of the facility you’re designing for? If it’s a typical office/building, strange that they would recommend straying from standard practice? Is there some sort of increased risk to the system that requires armored cable?
Its a control room with typical standard circuits; lighting, sockets, showers, heaters etc. His method and mine both pass all Amtech tests but I just don’t get why he is insistent on his method. When questioned he simply states that it will save time and money on the programme, but I just do not see how.
Sounds like he’s adding components and armoured cable for no good reason? Wouldn’t that increase the cost/labour? Unless it’s modular or intended to be temporary?
I canvassed my brother who is indeed an electrician. He sucked his teeth and said it sounded expensive but he’d do it for a good price.
I agree with you (and your brother) he just thinks it will save time and money. Personally, i think he is barking mad but he’s informed the client that they should instruct us that this should be the method of installation – which they did this morning.
Rob, presumably there is a shorter length of cable to terminate into the fitting. If the cable is particularly large it may be easier to install the shorter length from the junction box, which may save time and labour cost, but beyond that I am also a bit mystified. I will give Marsh a prod tomorrow.
Hi Rob
Could you please e-mail me a drawing of the system you are describing, or give me a ring to discuss it. It seems to me, if I am reading this correctly that this is an unsafe way of installing cables.
Hi Rob
A sketch would help! Is the intent is to take conductors back through the multicore to the DB where an armoured cable would be needed? I can see the utility in combining as much as possible into a multicore cable but only if you can provide phase and a dedicated neutral for all of the final circuits in the room – it could save time as you are only chasing a single cable back to the DB.
I would question how the earth will be provided however, check BS 7671 for full details but the CPC is normally split at the MET and then each circuit has a dedicated CPC thereafter; the exception would be if the cable is used as a sub main.
Can you give us a bit more in the way of a description? number of cores in the multicore? Final circuit voltages?
For some reason I cant paste a sketch into a reply so I’ll send via email.
Essentially the final circuits are standard ring mains and lighting circuits. There is no intention of utilising the neutral/earth from the armoured cable for the circuits in the rooms, the armoured cable is to be fully terminated in every junction box.
In terms of safety I don’t believe that it is unsafe, but am happy to discuss further and am interested to hear why that might be the case.
I am clutching at straws – as I agree with the general confusion expressed by many. Has the armored cable spec come from somewhere – is there some efficiencies to be made by using armored cable throughout as it is a requirement somewhere in the project? I.e. bulk purchasing and repeating the same install throughout – I think this is unlikely – but an idea.
The other bit is – “less joins” is always better; is the inclusion of junction boxes and diverging from standard circuits likely to decrease the number of connections required? Maybe by rationalizing the circuits. Again; I think this unlikely.
Lastly – please can you get him to explain his advice?
Just to put this one to bed. Skanska have submitted an official complaint to EDF/GE regarding the consultant. They have stated that his role is not to “police” the project and that he is actively obstructing progress.
Several of his recommendations have been incorporated into the design however, he has since changed his mind and questioned their inclusion! This has put time on the programme and increased cost. Skanska are unhappy as we cannot turn the designs around (based on his recommendations) in time to hit agreed milestones.
I think he is going to be sent on his merry way.