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

baldsparkies · Jun 4, 2011

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 · Jun 4, 2011

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 · Jun 5, 2011

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

Tony said:
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 · Jun 5, 2011

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 · Jun 5, 2011

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.

baldsparkies · Jun 5, 2011

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

Engineer54 said:
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.

Have always thought this to be 100% a statement of fact. In truth not always so.
I have seen a 120mm run together with a 95mm. I questioned it, as you would, and found it to be subject to a recorded departure.
The conditions relating to design and construction had been met by calculation ie the smaller of the two cables had been proven to be capable of handling its share of the loadings required, in relation to the overcurrent protective devices ratings, disconnection times, discrimination, and a whole bunch of calcs. (This was done by an electrical consultants agency)
I was on site with an niceic inspector at one point for a different reason, but whilst with him. pointed this out, He read the specs and agreed it was perfectly acceptable as a departure because the consultant had proven suitability of the install.
I learnt something that day

Thats the great thing about the trade, you never stop learning.

Its suprising how we can make a blanket style assumption, and apply it through out our working lives and then one day, find all is not as black and white as we had thought.

Engineer54 · Jun 5, 2011

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

johnboy6083 said:
a UPS sytem i fitted recently, was on line 100% of the time. i believe that it powered the instrumentation and telemetry.

All UPS systems are ''On-Line'' 100% of the time, otherwise they wouldn't be uninterruptible!! The battery back-up side of things however, is not... They will be only be receiving a trickle charge during normal mains supply to the load.

Engineer54 · Jun 5, 2011

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

baldsparkies said:
Have always thought this to be 100% a statement of fact. In truth not always so.
I have seen a 120mm run together with a 95mm. I questioned it, as you would, and found it to be subject to a recorded departure.
The conditions relating to design and construction had been met by calculation ie the smaller of the two cables had been proven to be capable of handling its share of the loadings required, in relation to the overcurrent protective devices ratings, disconnection times, discrimination, and a whole bunch of calcs. (This was done by an electrical consultants agency)
I was on site with an niceic inspector at one point for a different reason, but whilst with him. pointed this out, He read the specs and agreed it was perfectly acceptable as a departure because the consultant had proven suitability of the install.
I learnt something that day Thats the great thing about the trade, you never stop learning.
Its suprising how we can make a blanket style assumption, and apply it through out our working lives and then one day, find all is not as black and white as we had thought.

I'd really like to see that calculation...haha!! ....That's an absolute first for me!!

If that was the case, then 2 x 95mm would have surely been more appropriate to have been used!!!

baldsparkies · Jun 5, 2011

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

Agreed, as usual though I reckon costings must have played a part.
The original was the 120mm, 95mm was an added upgrade The 95mm was capable of handling over 50% of the total design current.
There was a lot more to it than that though. The company was reputable and the NICEIC inspector was in his fiftys and new his stuff so Im not going to argue the point cus i would soon be out of my depth.
The point is if a consultancy and the niceic say its good as a departure then surely they must have a point ???
Like I said it was news to me to but I have seen it on two seperate occassions now.
This was the only one with paperwork though.

Engineer54 · Jun 7, 2011

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

baldsparkies said:
Agreed, as usual though I reckon costings must have played a part.
The original was the 120mm, 95mm was an added upgrade The 95mm was capable of handling over 50% of the total design current.
There was a lot more to it than that though. The company was reputable and the NICEIC inspector was in his fiftys and new his stuff so Im not going to argue the point cus i would soon be out of my depth.
The point is if a consultancy and the niceic say its good as a departure then surely they must have a point ???
Like I said it was news to me to but I have seen it on two seperate occassions now.
This was the only one with paperwork though.

As i said, i'd of liked to see those calculations!!! Something is very wrong if the smaller CSA cable, can handle over 50% of the design current. What about any fault current analysis on this set -up ?? ...Frankly a simple departure notice is just not on, ...Two different sized cables run in parallel as one cable, does not conform to the universal criteria of a parallel run supply...

To be honest, i can't see why any decent consultancy firm would even get involved, in trying to substantiate such a supply method. As for the Niceic Inspector, .... Did he bother to go through and check those calculations, or did he take them at face value??

baldsparkies · Jun 23, 2011

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

Engineer54 said:
As i said, i'd of liked to see those calculations!!! Something is very wrong if the smaller CSA cable, can handle over 50% of the design current. What about any fault current analysis on this set -up ?? ...Frankly a simple departure notice is just not on, ...Two different sized cables run in parallel as one cable, does not conform to the universal criteria of a parallel run supply...

To be honest, i can't see why any decent consultancy firm would even get involved, in trying to substantiate such a supply method. As for the Niceic Inspector, .... Did he bother to go through and check those calculations, or did he take them at face value??

When push comes to shove you see what you see, read what you read, listen to others opinions, and then do what you consider to be the right thing.
This in mind I am running a parrallel sub myself over the weekend. Existing is 95mm and additional will also be 95mm, thats how I have always done it and always will. I am not saying that calcs ect may or may not prove otherwise from time to time, but you have to leave a job feeling good about the way you have done things.
No doubt I will see parrallel feeds of different sizes in the future, but they won't be my installs.
That way I don't need to address a departure or justify it.

Thanks for your input E54.