question

ejrossouw avatar image
ejrossouw asked

Is 60 degrees C excessive on a 200A Mega fuse holder terminal?

When a customer's 5KVA MP-II system runs under full load for prolonged periods (read heating hot tub etc.), the terminals on the holder get 60 degrees C although the 70mm2 cables are just warm. Connected and tightened as per the instructions. The terminals on the MP-II also seem a touch hot but I don't actually have a reference as to what is reasonable? Any field experience input appreciated.


mega fuse terminals very hot
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klim8skeptic avatar image klim8skeptic ♦ commented ·
I would probably measure the voltage drop across the cable \ fuse assembly.
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ejrossouw avatar image ejrossouw klim8skeptic ♦ commented ·
We have done, but it cannot hurt to check it again.
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2 Answers
wkirby avatar image
wkirby answered ·

Does the fuse holder have adequate cooling? If it is in a small enclosure without air circulation it could over heat.
Cold resistance is about 0.26mΩ, which will increase with temperature rise.
Assuming it is a 48V MultiPlus at full load, that would be 2.6W of heat being dissipated by the fuse when cold (room temperature I presume). As the fuse gets warmer it will dissipate more heat and so increases exponentially.

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ejrossouw avatar image ejrossouw commented ·
Thank you. It is installed in a domestic setting with adequate space/ventilation and to specification. The resistance on the fuse is something can check.
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Alexandra avatar image
Alexandra answered ·

@ejrossouw

Check your terminal torque.

Make sure the lug is the right size. Reduced contact area makes heat.

Hottest I have had with ambient at 25 deg C is 40. But it was terminal torque.

Edit:and arrangementnof lugs and fuse...?

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ejrossouw avatar image ejrossouw commented ·

Mega fuse terminal at 57 degree C

hotmegafuseterminal.jpeg

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hotmegafuseterminal.jpeg (360.0 KiB)
pwfarnell avatar image pwfarnell ejrossouw commented ·
I am not an expert on this so I may be talking rubbish. On your Megafuse terminals you have large washers between the spring washers and the lugs. These washers will spread the load from the nuts over a larger contact area so there will be a lower contact pressure on the lugs so less chance of the lugs deforming to form a good contact.
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ejrossouw avatar image ejrossouw commented ·

Temp Measurement

whatsapp-image-2022-08-05-at-43933-pm.jpeg

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whatsapp-image-2022-08-05-at-43933-pm.jpeg (14.8 KiB)
ejrossouw avatar image ejrossouw commented ·

Installation

whatsapp-image-2022-08-06-at-75521-pm.jpeg

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whatsapp-image-2022-08-06-at-75521-pm.jpeg (326.6 KiB)

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