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Thread: Cat 6 max voltage

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    Cat 6 max voltage

    I need to switch a relay 60 metres away from the point of supply it must be rated to power the relay coil 24/7 if it is left switched on.

    The output is 12 VDC, but I thought of using a relay and a 48 power supply, to boost the power to 48 VDC.

    I found this:

    This also got me thinking about all these cat 5e and cat cables in the same wireway as the power cables used for the CT.

    Peak operating voltage max. 90 V
    Voltage UL/CSA 300 V
    Testing voltage core/core 2000 V core/screen 2000 V
    Min. bending radius fixed laying: 5 x d flexible application: 10 x d continuously flexible: 15 x d
    Temperature range VDE VDE fixed laying: -40C/+70C VDE flexible application: -40C/+70C UL: up to + 80C
    Comments are my opinion, unless regulations are attached to support the comment. This is social media, not a court room.

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    Comments are my opinion, unless regulations are attached to support the comment. This is social media, not a court room.

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    Diamond Member AndyD's Avatar
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    The circuit resistance for a 60m run will be 10.4Ω and that's just resistance not overall impedance and that assumes no resistance at the terminations..... probably not the idea cable for a circuit of that length. I guess you could double or triple up on the conductors if you're not using them for anything else but CAT5e cables are made to perform well at high frequencies (several hundred MHz) not at 50Hz power frequencies or DC.

    Current transformers and their associated wiring are something of a special case when it comes to voltages present. If a current transformer is properly connected and installed the voltage on the wiring from its secondary will be low. If the CT is disconnected on its secondary side whilst it's primary is still installed on a wire with a high load then the voltage can runaway into the KV range which makes CT's in general a hazardous item for the uninitiated. Open circuit secondaries on a CT can lead to internal over-voltage damage to the CT and external flash damage to the contractor who disconnected it. Some CT's have built in safety protection (ref IEEE C57.13) to keep this runaway voltage to safe limits but many don't.

    TL/DR
    • I wouldn't use CAT5e cable for ELV DC supplies especially over long distances.
    • Unless they publish Uo/U voltage figures above 230v then the cable you're using isn't rated for installation in the same wireway as ≥230v electrical supply/control cables.
    • I personally wouldn't use the CAT5e cable in the same wireway as a CT cable because disconnection of the CT secondary either by accidental damage of by an unaware contractor is a forseeable possibility so the voltage could exceed the rating of the cable. That said I can't give you a reg to back that up.....
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    A wireless solution is not an option, I have a cat 6 cable installed so I need to find a way to control light 60-70 away from the building.
    Comments are my opinion, unless regulations are attached to support the comment. This is social media, not a court room.

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    Platinum Member Derlyn's Avatar
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    Can't you trigger an scr and use a latching relay ?

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    Diamond Member Justloadit's Avatar
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    If you are simply powering the coil of a relay, then there should not be an issue.
    Most 12V relays are less than 0.5W, which means a current of approximately 35mA.
    Coil impedance is around 350 ohms, so 10 ohms from the cable resistance is negligible.
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    I was going to fit a relay at the source, a 230/48 V power supply to supply a relay in the outbuilding.

    Instead I am going to run the 12 VDC to the outbuilding and fit as small 5 amp relay (power = 0.02), use the N/O contact to switch a 32 amp relay (power 0.35)

    I will test the volt drop tomorrow.

    Quote Originally Posted by Justloadit View Post
    If you are simply powering the coil of a relay, then there should not be an issue.
    Most 12V relays are less than 0.5W, which means a current of approximately 35mA.
    Coil impedance is around 350 ohms, so 10 ohms from the cable resistance is negligible.
    Comments are my opinion, unless regulations are attached to support the comment. This is social media, not a court room.

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