Total diameter of MV cable exceeds by 7 mm the diameter originally submitted to the end user 1

[Oblsss]

Hello to everyone!

Due to incorrect parameters setting during the sheathing/jacketing process of a medium voltage, a big part of the produced cable has a total diameter exceeding the one originally stated to the end user by nearly 10% (67 mm compared to 60 mm). As if that wasn't enough, the length produced is less than what the customer requested for a few meters ...
We plan to contact the end user to see if he will accept the produced length and to let him know about the difference in overall diameter.

I was thinking how a 7 mm difference could affect the installation/laying process or the end user:

1. if the installer uses cable rollers to lay the cable, maybe it would not fit the roller already purchased based on submitted data, assuming that the MV cable may be the biggest diameter in a
typical project.
what are the tolerances in mm for a typical cable roller?
2. if the installer uses a pulling head, this should be no problem since for single core cables it is usually fastened on the metallic part of cable.
3. if the installer uses a stocking type pulling grip, normally they have a tolerance of 20-25% in relation to the nominal diameter.
4. For the cable glands of the switchgear panel and the electrical load termination box, we are quite marginal to the commercially available tolerances.
I understand that in the case of the termination box, this can get really bad due to space limitations, ATEX enclosures for motors not allowing drilling bigger nut threads etc.

The above are some thoughts I have made before communicating with the end user. It would be great if anyone more experienced could comment on those or notice any important details omitted!!

postscripts

My job is in the design/tendering/commercial part and I don't have enough information about the mistake that led to such a deviation in the diameter.

Thanks in advance,

G.P.

 

[waross]

The pulling sheaves that I have seen for many years have a radius of about 2 inches, or 4 inches wide.
This is the radius that the cable rides in. Te wheels are available in a wide range of diameters, from 2" to 36" or more.
Pulling hardware will fit a very wide range of sizes.
Of more concern is the cable glands.
There is not much leeway in gland sizes.
In the worst case the next larger diameter gland connector may require a larger entry hole.
If the entry is a threaded hole in a cast enclosure, the issue becomes more serious.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dpc]

I'd be equally concerned about the short length if this is intended to be a single run. If they plan to use cold-shrink or heat-shrink terminations, those kits must be properly sized to the overall size as well. It might be workable, but if I put myself in the customer's shoes, I'd be inclined to say no thanks - you can keep the cable. If you offer them 50% off it might help.

 

[Oblsss]

Thank you very much for your answers!

@ dpc

As far as heat-shrink terminations are concerned, how would a larger overal diameter (let's consider a 10% deviation) of the cable cause problems to the installer?
Bear in mind that according to the x-ray measurements during the insulation of the cable core, the values until the cable jacketing/sheathing are really close to the ones stated to the end user!

G.P.

 

[davidbeach]

Why is this even a discussion? Why isn't a new batch of cable being produced that meets spec? Customer said what they wanted, you accepted the order saying you could produce the specified product within the specified tolerances. It sounds like you failed. Seems to me like it's up to you to make it right, not to try to figure out why the customer should accept delivery of something other than what they ordered. The lack of overall quality control may be a much larger issue than the the extra 7mm of overall diameter. And short? Wire should never come out short, there should always be a bit more then need in any length of wire until it's cut for the final terminations.

 

[dpc]

The terminations are listed for application over a certain range of cable sizes. If applied outside that range, there would be no warranty, and in the US it would violate the National Electrical Code and be illegal.

I can't say if it would be an issue in this particular case.

 

[7anoter4]

40 years ago I worked in a cable factory as a design engineer for [cable] products and production equipment.
An oil distillation company ordered a large quantity of 10 kV cables. At the same time, this company ordered all the necessary accessories - mainly cable glands - for the hazardous location based on the cable diameter in the table in the cable company's catalog.
The cable has been ordered and tested according to IEC 60502-2. No outer diameter is required according to this standard.
The overall cable diameter was calculated as per Annex A of the above standard:
Annex A [normative] Fictitious calculation method for determination of dimensions of protective coverings
From this annex it is quite understandable:

So, if the people at the oil company had consulted with us, we could have advised them first to measure the actual diameter and then to order the glands

 

[waross]

I was on a site years ago where the contractor used ACWU cable instead of TECK cable.
ACWU, Armoured-Cable-Wet-Underground. Constructed of a spiral armour over the conductors and a plastic jacket.
TECK, A similar cable but with the addition of a fairly thick sheath over the conductors and under the spiral armour.
The contractor correctly determined the overall diameter of the cables and pre-ordered gland connectors from the TECK page of the catalogue.
For a given conductor size and number the overall diameter of TECK cable is greater.
All of the glands would fit the cable diameters, but in many sizes, the conductors would not pass through the throat of the connectors.

Bill
--------------------
"Why not the best?"
Jimmy Carter