Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessories

[baldsparkies]

Have been concerned about an install thats running on the warm side.

MCCB is rated at 200 250A supply cable is supposed to be 95mm swa (4 Core) which surprises me looks more like 70mm at best 50mm worst. Nothing on the side wall (Darn those manufacturers)

Now the MCCB has a design operating temp of 65 degrees and the tech dept as confirmed that table 4D4A not 4E4A should be used for cable sizing and current ratings.
The logic being that whilst 90 degree thermoplastic offers a higher design current Table 4D4A should be used to keep the temps within the design limits of the connected devices. Also with the MCCBs the max currents do drop off considerably as temps increase.
All this makes perfect sense, but my main concern is a supposed 95mm cable running hot to the touch when only pulling 170 amps per phase. If 95mm we should be looking at 304A with xlpe or 251A with the 70 degree.
Connections are all good so would you guys be of the same thoughts as me ie 95mm + 170 amps = cable running at close to ambient temp, not blimey thats getting warm WTFs going on here.
Thanks for your thoughts on this one my learned friends, always nice to have second opinions.
I deffo am going to try and get the cable sizing verified asap. Will be armed with a set of calipers and checking the outer diameter which i think should be around 41.7mm. if its a 95mm cable might check lug sizing as well

 

[Deleted member 26818]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

Sounds dodgey, what's it feeding?

 

[baldsparkies]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

Sounds dodgey, what's it feeding?

UPS and IT data racks, don't think it should be running warm to hot though, not if its a 95mm no way.
trouble is swa sizing is a pain, when your just looking at it. I still get it wrong sometimes and ive been doing it long enough.
trouble is the overaul diameters vary by only a few mm from one size lower to one size higher. especially if by different cable manufacturers

 

[Deleted member 26818]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

Could there be harmonics causing the heating?
Is it possible to measure the resistance, and then work out the CSA from that?

 

[baldsparkies]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

Could there be harmonics causing the heating?
Is it possible to measure the resistance, and then work out the CSA from that?

Can't power down spin, Only an 8 metre run as well.
I honestly think the cable is a 50mm it just looks to small to me. if so everything would start to make sense, as said, 170 amps just aint going to run hot through a 95mm cable, Connections are tight and on such a small run almost free airspace on a cable tray somethings not adding up. Harmonics are present yes but negligable ups has inverters and they always like to make themselves known lol.

 

[Deleted member 26818]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

Sounds like you are going to have to run a larger cable.
How long will the UPS last?

 

[baldsparkies]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

Not long enough Spin but its genny backed so no probs there.
They have been told the installed cable is rated at 300 amps.
To be honest if they start adding loads to anywhere near that I reckon I will be making cups of tea on the blooming thing.
I dont like the way all the quoted figures being supplied to them are at max ratings.
Thats what they are intending loading to, so no margin for error or unknown variables.
These things are running 24-7 so you cant allow for any diversity.
Will get back when I have sussed it, but thanks for your input Spin much appreciated.

 

[Mark_Burgess]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

Is there any chance of opening the DB and measuring the OD of one of the conductors without powering down?
Maybe its time they run the back up genny as it should once in a while and that will give you the opportunity to check.

 

[benji]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

can you get a look at the lugs to see whats stamped on them

 

[Knobhead]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

If the UPS will allow time, disconnect and have a look at one of the lugs. Hopefully some markings will be clear enough to read. Have you taken a temperature measurement of the cores near the breaker? If they’re in tolerance I’d leave well alone.

I’ll admit trying to identify modern cables with compressed cores and XLPE insulation is a pain in the a*se.

 

[baldsparkies]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

Ok, I have confirmed cable size as 95mm. The temp of the outer sheath (Not the core) is 42 degrees. but the core will obviously be running warmer than this.
Although the cable is XLPE and ratings have been taken for 90 degree thermo insulated ie max rating 304 amps. My understanding is that you have to take into account the heat transfer to the overcurrent device ie the MCCB. This being the case, you should be looking at a maximum operating temp of 65 degrees. as per manufacturers guides. Its surprising how quickly operating temperatures start to affect the nominal current of the MCCB. As an example at 45 degrees nominal current drops to 244 amps 55 degrees 231 amps, and 65 degrees which is the max temp permitted we are looking at 219 amps.
At the moment the cable is pulling 170 amps. I feel the cables max loading should be based on table 4D4A which would de rate a 95mm to 251 amps and not the 304 amps that table 4E4A quotes. that way the design current will prevent the overcurrent device exceeding its 65 degree limit give or take 5 degrees.
Do you guys see where I'm coming from with this or am I missing something.
My concern is that the customer thinks the cable can take 300 amps, and technicaly it can but in practice I feel you need to look at the bigger picture, ie you have to consider connected equipment ???
Harmonics volt drop and core temperatures can catch you out when running higher currents. Also I never like the idea of maxing out cables just cus its written in the charts. You need some leeway surely.
Maybe Im getting old lads

 

[ACDC]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

Bit of a long shot, would it be worth considering running a parallel feeder cable along side the existing 95?(Space permitting) should reduce operating temperature and any future additions to the circuits will be covered. Just my tuppence worth.

 

[Knobhead]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

Yes I do know where you’re coming from. Trying to turn off a 1200A switch that the cables had been running hot on was no joke. It was “yes we know they’re hot, but we can’t afford to do anything yet” went on for years. When two of us swinging on the switch handle couldn’t get it to shift something had to be done. A third .3 paper lead sorted it.
It was like talking to the doorframe, no sorry, I’d have got more sense out of the doorframe for years.
The feeder fuse switch from the main board was only 800A but had had 1000A fuses shoehorned in to it, that was toasted and so had to be replaced with an ACB.

People don’t realise the effects of imported heat.

 

[Guest123]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

This is quite a common problem that I come across more and more, particularly when the installed cable is the XLPE type.

Most assume that because the cable is rated to operate at 90dC, all switchgear is fine to do so also. It is simply not the case and nearly all switchgear manufacturers will advise the same.

IMO a slected cable for install shouldn't be relied upon to work at it's maximum operating temperature regardless of manufacturers specifications for the reasons we see here.

 

[baldsparkies]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

This is quite a common problem that I come across more and more, particularly when the installed cable is the XLPE type.

Most assume that because the cable is rated to operate at 90dC, all switchgear is fine to do so also. It is simply not the case and nearly all switchgear manufacturers will advise the same.

IMO a slected cable for install shouldn't be relied upon to work at it's maximum operating temperature regardless of manufacturers specifications for the reasons we see here.

Totaly agree,
The manufacturers position on maximum operating temps for overcurrent devices protecting the cables should always be given a primary consideration, to much emphasis is often applied to the cable ratings and temps. Copper is a good conductor for power transfer, but that also holds true for heat. And the damage created over time as been witnessed by a lot of us here.

Thanks to you all, for your advice and help.

 

[baldsparkies]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

One point I feel worthy of consideration. All this heat build up is usually down to bad or inefficient design somewhere down the line.
Often a major missed point is a lack of capacitance in circuits that are highly inductive.
Could I be not to far off the mark when I say that applied power factor correction at the mains position could have a marked improvement on the running currents and heat build up on an installation such as this. ??

 

[Knobhead]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

To reduce PF loading in a cable the correction needs to be at the load end.

 

[baldsparkies]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

To reduce PF loading in a cable the correction needs to be at the load end.

Tony where the larger modern UPS systems have been installed, would the manufacturers normally include PF correction within the units then.
I am thinking of the affect the inverters would have on the install at the load end. If so, then my thought would tend to be, any additional parrallel PF correction (supply side) wouldn't acheive much between the KVA KVAr offsets.
The only way forward is to simply run a parrallel cable of the same csa lugged and fed from the same MCCB.

 

[Engineer54]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

Depends on what type of UPS system you have there?? Conventional UPS systems will usually only have inverter in circuit when under Battery power. In general use the supply will normally be run through an isolation TX to the load. Obviously there's a lot more involved than that in a UPS module, ...there will be smoothing an voltage control etc, etc, you will need to study the maintenance manuals and the like for your specific UPS system...

To run a parallel cable, you will first need to ascertain what the original cable size is, as you know, you cannot have two different cable sizes run in parallel as a single cable.

 

[johnboy6083]

Re: Safe operating temperatures XLPE 90 degree vs table 4D4A for connected accessorie

a UPS sytem i fitted recently, was on line 100% of the time. i believe that it powered the instrumentation and telemetry.