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RE: LSOH v PVC [Hevacomp Forum]

tony hutchison
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Duncan
 
many thanks for the prompt response.
I've read that section but unfortunately it still doesn't answer my query and it may well be that i'm not understanding what the Hevacomp takes into account with an LSF cable versus a PVC cable, but perhaps if I explain an example as follows
 
if I have a 25A MCB protecting a 2.5mm LSF single cable installed in trunking / conduit, then that cable is capable of carrying 31A (90deg thermosetting insulation)
if I have a 25A MCB protection a 2.5mm PVC cable installed in trunking / conduit, then that cable is capable of carrying 24A (70deg PVC insulation), therefore non-compliant
 
so the LSF cable has (for the same copper conductor) has a better current carrying capacity due to the temperature rating of it's insulation.
 
if the LSF cable is sourced from and/or connected to a protective device and/or accessories which does not share that enhanced operating temperature, how can we then benefit from that cable
 
Regards,
 
Tony
 
 
Tony Hutchison
Electrical Engineer
City Development - Design & Property Division
Floors 5/6 Dundee House
50 North Lindsay Street
Dundee DD1 1LS
Tel, 01382 433264
e-mail: tony.hutchison@dundeecity.gov.uk


-----"Duncan Brown" <bounce-83D79C23-3DDB-497D-B2E2-B5CB87B1BC6C@communities.bentley.com> wrote: -----
To: <HevacompForum@communities.bentley.com>
From: "Duncan Brown" <bounce-83D79C23-3DDB-497D-B2E2-B5CB87B1BC6C@communities.bentley.com>
Date: 19/07/2017 09:05AM
Subject: RE: LSOH v PVC [Hevacomp Forum]

 

Message from Bentley Communities
Duncan Brown

Hi Tony - The software doesn't force you to do anything. if the cable fails the checks you will get a report of the failures. It would be up to yourself to decide whether to use a different cable.

I would strongly recommend considering section 4.6 in the manual for details on how operting temperature are implemented. This is quite a detailed section and should be of help.

The manual can be accessed by running the Connect program, clicking on the file menu and selecting "manual" - the section that should interest you would be "17th Edition Calculations"

Regards,


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  • 0 Offline

    Tony – If a specific cable isn’t available that suits your requirements then you should consider a different cable that has similar characteristics. As the PVC cable doesn’t meet your requirements you should consider an equivelent other cable.

    Duncan Brown



  • 0 Offline
    Duncan
     
    i'm afraid this answer doesn't help at all.
     
    we would never chose a PVC insulted cable, certainly not as a final wiring circuit cable, perhaps only as an outer sheath of a buried armoured cable, so as a matter of course it would be LSF and the question i'm asking is whether we can use such a cable and benefit from its characteristics whilst these directly attributed to the higher operating temperature, which is not shared by either a circuit protective device or an accessory, which the final circuit may be connected to.
     
    so does Hevacomp take into account with an LSF cable versus a PVC cable, the scenario as follows
     
    if I have a 25A MCB protecting a 2.5mm LSF single cable installed in trunking / conduit, then that cable is capable of carrying 31A (90deg thermosetting insulation)
    if I have a 25A MCB protection a 2.5mm PVC cable installed in trunking / conduit, then that cable is capable of carrying 24A (70deg PVC insulation), therefore non-compliant
     
    so the LSF cable has (for the same copper conductor) has a better current carrying capacity due to the temperature rating of it's insulation.
     
    if the LSF cable is sourced from and/or connected to a protective device and/or accessories which does not share that enhanced operating temperature, how can we then benefit from that cables characteristics
     
     
    Regards,
     
    Tony
     
     
    Tony Hutchison
    Electrical Engineer
    City Development - Design & Property Division
    Floors 5/6 Dundee House
    50 North Lindsay Street
    Dundee DD1 1LS
    Tel, 01382 433264
    e-mail: tony.hutchison@dundeecity.gov.uk


    -----"Duncan Brown" <bounce-83D79C23-3DDB-497D-B2E2-B5CB87B1BC6C@communities.bentley.com> wrote: -----
    To: <HevacompForum@communities.bentley.com>
  • 0 Offline in reply to tony hutchison

    Hi Tony, are you saying that you want to use the LSF cable but somehow limit it's operating temperature to 70deg to match the device and connected equipment?

    In terms of the software cables are initially sized based on the current carrying capacity defined in the data. This is assumed to be a loaded cable and therefore the cable will be assumed at operating temperature. Adjustments are made for grouping, ambient temperature etc but there is not adjustment in initial cable sizing for operating temperature. Duncan has already pointed you to the section in the help files for details on that.

    Cable Initial and Final temperatures do come into play in the Volt Drop and Fault Current Calculations but I don't think this affects what you are asking.

    To take advantage of the capacity of LSF you set it as you chosen cable. We don't hold any details of device operating temperature in the data and so we don't do any check against the cable operating temp to check validity. We leave that to the discretion of the engineer.

    Steve Brown | Bentley Systems

  • 0 Offline
    duncan
     
    maybe this will better explain the issue
     
    BS 7671
     
    Regulation 512.1.5 (and note 1 of Table 4E1A) states that Switchgear, protective devices, accessories and other types of equipment shall not be connected to conductors intended to operate at a temperature exceeding 70 degrees at the equipment in normal service (LSZH in this case) unless the equipment manufacturer has confirmed that the equipment is suitable for such conditions, or the conductor size shall be chosen based on the current ratings for 70 degrees cable of a similar construction (i.e. PVC)
     
    Also Regulation 433.1.1 (ii) which states that the rated current or current setting of the protective device (In) does not exceed the lowest of the current-carrying capacities (Iz) of any of the conductors in the circuit.
     
    this effectively means that we cannot calculate with and LSZH (LSOH) type cable and we must then calculate with a PVC cable, however, as we would never specify a PVC cable we're then at the disadvantage of not being able to extract a circuit chart from the Hevacomp calculation, as it will refer to PVC and we would be specifying LSZH.
     
    is there anything we can do, to calculate in PVC (as BS7671 requires us to do), whilst we can print a circuit chart and refer to the cable as LSZH
     
    this is the issue and as this will apply to the whole of the UK (we all work to the same BS7671) we cannot then be the only people with this issue.
     
    Cheers,
     
    Tony
     
     
    Tony Hutchison
    Electrical Engineer
    City Development - Design & Property Division
    Floors 5/6 Dundee House
    50 North Lindsay Street
    Dundee DD1 1LS
    Tel, 01382 433264
    e-mail: tony.hutchison@dundeecity.gov.uk


    -----Tony Hutchison/CD/dundeecity wrote: -----
    To: <HevacompForum@communities.bentley.com>
  • 0 Offline in reply to tony hutchison

    Hey Tony - We don't have the data available for the LSZH cable that you require. Please see Steven Brown's reply, above.

    Regards,

    Duncan Brown



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