SAFETY ALERT, Perspex cased NVA BMU (Balanced mains unit)

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Toppsy
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#1 SAFETY ALERT, Perspex cased NVA BMU (Balanced mains unit)

Post by Toppsy »

Not sure anyone on here has one of these but if you have please take note this posting on AoS:

https://theartofsound.net/forum/showthr ... ains-unit)
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#2 Re: SAFETY ALERT, Perspex cased NVA BMU (Balanced mains unit)

Post by Nick »

It needed the input fuse rating fitted reported. That's about it. Some of the linked text is a bit over the top
Think about that.. 55 degrees above ambient. Usually a transformer has free air around it that conducts heat away from it.
Yes, think about it, under normal use a transformer should not generate much heat, the temp rating is normally related to the temp the transformer is enclosed in, not its own generated heat. The winding enamel is normally rated to at least 155C

I refer the comment to the fact that you often get transformers potted in epoxy or similar without the world ending due to the temperature rise.

The transformer should probably have a thermal trip built into its windings, and the fuse in the (being NVA) captive mains lead should have been fused according to the transformers size.
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#3 Re: SAFETY ALERT, Perspex cased NVA BMU (Balanced mains unit)

Post by Ray P »

I'm with you Nick, both with regard to the tone of the (original AoS) post and that an appropriately rated fuse should prevent the transformer generating that sort of heat.
Last edited by Ray P on Mon Jul 05, 2021 9:24 pm, edited 1 time in total.
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#4 Re: SAFETY ALERT, Perspex cased NVA BMU (Balanced mains unit)

Post by Nick »

(BTW Colin, my comments refer to the linked post, not the fact you posted a link).

To sum it up. Something failed and nothing bad happened :-)
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#5 Re: SAFETY ALERT, Perspex cased NVA BMU (Balanced mains unit)

Post by Toppsy »

Nick wrote: Mon Jul 05, 2021 8:16 pm (BTW Colin, my comments refer to the linked post, not the fact you posted a link).

To sum it up. Something failed and nothing bad happened :-)
That is how I read your reply Nick.
Just caught up with your reply and that of Ray. I've been listening to a new double album LP Simon bought me to help me relax now I'm back home.
I did wonder about potted TX's when I first read the AoS link, and that something the guy posted didn't seem quite right. But you know my limited knowledge of electronics hence the main reason I build speakers.
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#6 Re: SAFETY ALERT, Perspex cased NVA BMU (Balanced mains unit)

Post by savvypaul »

The owner's wife plugged her 4kw 'steam iron station' into the BMU.

Our current BMU has a thermal cut-out. It will save the unit from your wife, but it will not improve her ironing.
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#7 Re: SAFETY ALERT, Perspex cased NVA BMU (Balanced mains unit)

Post by Ray P »

savvypaul wrote: Thu Jul 29, 2021 12:35 pm The owner's wife plugged her 4kw 'steam iron station' into the BMU.

Our current BMU has a thermal cut-out. It will save the unit from your wife, but it will not improve her ironing.
...as would a correctly rated fuse.
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#8 Re: SAFETY ALERT, Perspex cased NVA BMU (Balanced mains unit)

Post by savvypaul »

Ray P wrote: Thu Jul 29, 2021 12:46 pm
savvypaul wrote: Thu Jul 29, 2021 12:35 pm The owner's wife plugged her 4kw 'steam iron station' into the BMU.

Our current BMU has a thermal cut-out. It will save the unit from your wife, but it will not improve her ironing.
...as would a correctly rated fuse.
Of course.
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#9 Re: SAFETY ALERT, Perspex cased NVA BMU (Balanced mains unit)

Post by Nick »

Just thinking about this, I am not sure how a 4kw load is ever allowed on a 13A plug.

But I would have expected the BMU to have a 10A fuse in its plug (just under 250% of primary current), so that should have blown. For that matter the 13A fuse should have blown assuming the "4kw" load was fitted with one.
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#10 Re: SAFETY ALERT, Perspex cased NVA BMU (Balanced mains unit)

Post by Neal »

yup seems unlikely unless it was one of these!

https://www.ironingsupplies.com/Equipme ... 99c87.html. but this requires 2x 13 amp sockets
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#11 Re: SAFETY ALERT, Perspex cased NVA BMU (Balanced mains unit)

Post by savvypaul »

Nick wrote: Thu Jul 29, 2021 12:59 pm Just thinking about this, I am not sure how a 4kw load is ever allowed on a 13A plug.

But I would have expected the BMU to have a 10A fuse in its plug (just under 250% of primary current), so that should have blown. For that matter the 13A fuse should have blown assuming the "4kw" load was fitted with one.
A 10A fuse is fitted to new BMUs. What was fitted in the unit concerned, I don't know for certain. The owner refused to send the unit to us for inspection.
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#12 Re: SAFETY ALERT, Perspex cased NVA BMU (Balanced mains unit)

Post by savvypaul »

Nick wrote: Thu Jul 29, 2021 12:59 pm Just thinking about this, I am not sure how a 4kw load is ever allowed on a 13A plug.
I'm quoting the owner...
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#13 Re: SAFETY ALERT, Perspex cased NVA BMU (Balanced mains unit)

Post by Nick »

Yep "Standard single phase operation (requires 2 separate 13amp sockets)" but if it was in a extension lead, they could have plugged both into the same 4 way (for example). In which case the BMU may have done them a favour and pointed out the folly of doing that.
Little known fact, coherent thought can destructively interfere with itself leaving no thought at all, that’s why I prefer incoherent thought.
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