A few fusing questions on UK gear here in the US

[Goodizzy]

Good morning-

I'm attempting to stockpile mains AC fuses for all the early UK transistor receivers and amps I have. (Leak, Armstrong, Rogers, etc.) As I am in the US and all my equipment has several primary PT taps, I run all on 120V. The majority use 5x20mm fuses.

Instead of replacing the BS1362 plugs with non-fused US 3-prong cords, I have been keeping these in place and running them into an appropriate Euro/UK surge protector. Most have various sized fuses from 3A up to 13A across hot in the BS1362 plug.. Since we don't fuse plugs here in the US, is there a particular current rating I should use? 3A, 5A, etc.? I assume these should be HBC ceramic fuses as well? And they are the larger, 6x30mm fuses?

I have read the sticky on fuses and while I am no professional I believe I have somewhat a grasp on the electronics behind it. I understand the plug fuses to only be there to protect the wire from receptacle to appliance in case of fire, so I would like to protect this valuable equipment as much as possible!

My only concern is the difference in grounding and wiring in the US vs. UK. Any input would be greatly appreciated Regards,

Chris

[paulsherwin]

The UK uses 30A 240V ring main circuits, originally protected by 30A wired fuses in the consumer unit (now largely replaced with circuit breakers). A faulty appliance could pull up to the full 30A before the consumer unit tripped, which is much too much for a line cord.

The plug fuse is to protect the line cord in this system. A wide range of fuse sizes have been supplied in the past, but the common ones are 3A, 5A and 13A. The plug fuse isn't there to protect the appliance.

Most consumer electronics should be fitted with 3A fuses, though 5A is sometimes used where there is a big inrush surge.

The plug fuse won't be doing much in an American system, where each radial circuit is individually protected, so it doesn't much matter what value you fit.

You can buy plug fuses from a large number of UK outlets, but beware of Chinese fakes (though this is less important in your case). I don't know if they're available from US sources, but even if they are they will be very specialist, and it will probably be cheaper to order them from the UK.

British people rarely buy plug fuses, because they rarely blow and can be scavenged from scrap electrical appliances.

https://en.wikipedia.org/wiki/AC_pow...gs_and_sockets

[high_vacuum_house]

Good afternoon,
You have to be careful if you buy BS1362 on EBay due to fake copies. I bought some once and wished I hadn’t. They looked identical and had a reputable company name printed on them though I was suspicious when I looked closely at them. I broke one open and found no arc suppressing sand inside. I binned the lot and instead bought them from RS components who definitely would not sell suspect safety critical parts. Also RS sell 1A and 2A BS1362 fuses which are not often found but a better rating than 3A fuses for low power devices,

Christopher Capener

[paulsherwin]

The Bussmann brand is frequently faked.

It's possible that Mouser sell them given that they have a UK facing portal priced in pounds, but I haven't investigated.

[Goodizzy]

Thank you for the easy to understand explanation! Much appreciated!

After browsing RS components it seems it would be too expensive with shipping to get these fuses. I had never really browsed the various 125V 15A replacement plugs before, only having a few cheap ones from the local hardware store that offer no strain relief.

As the fuse doesn't seems necessary due to the grounding of US systems, I think it might be best to just replace all BS1362 plugs with a better securing US plug. I am currently looking at Leviton and Edison plugs with good strain reliefs.

Edit: One final thing- I will still be order more ceramic 5x20mm AC mains fuses of the "slo blo" type for the PT mains fuses in the amps. Is it also safe to assume that the Chinese have flooded the market with sandless knockoffs of these as well? I have used mouser, digikey and MCM in the past, so maybe these places would be a better place to go than fleabay?

[paulsherwin]

Internal fuses are not normally sanded.

I agree that fitting US plugs is the sensible way to go, unless you somehow want to emphasise the 'Britishness' of the whole setup.

By the way, BS1362 is the standard for the plug fuses. BS1363 is the standard for the actual plugs and sockets.

[electrogram]

The fuses used in UK plugs are 25mm - 1" . 30mm - 1¼" are usually glass and used in the piece of equipment, from the 1930s into the 80s

[Goodizzy]

So glass time delay for AC fuses internal to the equipment, then?

[Bookman]

Yo Chris,
I cant help thinking that you may be opening up a can of worms. In this, let us not forget the difference in the ratios associated with our supply Voltages but also any capacitive and inductive reactance and the 2 Pi F constants associated with their calculation. It follows does it not that a device that consumes 1 ampere at 240 Volts will not necessarily consume 2 Amperes at 120 Volts.
Suffice it to say that perhaps an ammeter in circuit would be the only practicable method of determining fusing characteristics associated with your wishes.

[Ed_Dinning]

Hi Chris, I take it from your posting that you are running UK equipment through a transformer from US mains stepped up to 240V. If this is correct then a fuse fitted in the 13A plug would "see" UK conditions.

The (bad) thinking in the UK is that 13A plug = 13A fuse, WRONG. Depending on the appliance that is connected and it's cable size it may have as low as a 1A fuse fitted.
1, 2, 3, 5, 7, 10A fuses are available in the UK. They are often of an HRC construction and as far as I know are not available with a time delay curve.

For most practical purposes you should be able to use a 2 or 3A plug fuse to give good protection without fuse blowing on surges.

Ed

[Ed_Dinning]

Hi Chris, I take it from your posting that you are running UK equipment through a transformer from US mains stepped up to 240V. If this is correct then a fuse fitted in the 13A plug would "see" UK conditions.

The (bad) thinking in the UK is that 13A plug = 13A fuse, WRONG. Depending on the appliance that is connected and it's cable size it may have as low as a 1A fuse fitted.
1, 2, 3, 5, 7, 10A fuses are available in the UK. They are often of an HRC construction and as far as I know are not available with a time delay curve.

For most practical purposes you should be able to use a 2 or 3A plug fuse to give good protection without fuse blowing on surges.

Ed

[Goodizzy]

Thanks for the continued input, it is most appreciated! The "solid state" UK receivers/amps I have are:

-Leak Stereo 30
-Leak Stereo 30+
-Armstrong 525
-Armstrong 526
-Rogers Ravensbourne

All of these receivers/amps have a voltage selector for PT primary taps between 110V-240V. All except the Leak amps have manufacturer's manuals which indicated the appropriate sized fuse to use if you are NOT running on 240V mains. I have been using these manuals as well as looking at manufacturer's schematics or parts lists for the amps to determine the appropriate sized fuse to use. I have had no problems so far. Also, I only have two full receiver/speaker systems in my house, but have the ability, (and forgiving spouse!) to expand that up to four, which is why I am trying to get this under wraps.

I have run several of the amps on a step-up at one time but am slowly trying to ease myself back to using our 125V mains standard here. I have been checking DC voltages against the schematics to determine whether or not a bump transformer is necessary as the mains wall voltage has increased +-15V since the 60s here in the US.

The only manuals that are not explicit in fuse ratings for 125V are the Leak manuals, and I had a 1.6A fitted in the Stereo 30 plus AC fuse, (called for in schematic) for around a year with no adverse effect or blown fuses. (A 1.6 was in both AC and DC fuse positions!) Of course, I never go beyond about halfway on the volume control with the sensitive speakers and with the non-recapped amp.

After taking Paul's advise into consideration, I thought that it would be much easier to just replace the UK plugs with US 125V 15A plugs or else re-solder a whole new cord/plug into the equipment. This is due to the fact that he explained how each radial circuit is protected in US house wiring. The plug fuse, then, seems to be a non-issue and not necessary.

I am only an amateur hobbyist, but have been fiddling with these things for several years and am certainly open to being corrected if I am in error here.

[paulsherwin]

I really wouldn't worry about these fuses too much. Their main purpose is to stop your house burning down in the event of a catastrophic fault. It doesn't matter if the fuse is 1A or 3A in those circumstances as it will still blow. Just follow the manufacturer's instructions, and if there aren't any available then use common sense.

[pmmunro]

The attachment is a data sheet on BS1362 fuses. It is worth noting that, like most small fuses, their characteristic curves start at 1.6 times the rated value, For example, a 10A fuse will blow at 16A, but take 700 seconds to do that at this current. The time gets much shorter as the current rises and the fuse blows in 0.1 seconds at 180A.

180A is not at all an unrealistic current; the maximum permitted earth loop impedance for a ring circuit protected by a 32A Type B circuit breaker is 1.37 ohms at which 168A would flow. In most cases ELIs lower than 0.5 ohms will be normal, so the prospective fault current would be 460A. Lower ELIs still are not unusual.

Because of these high prospective fault currents, mains fuses within equipment should be high breaking capacity types as they will have to carry this order of current in the event of a short circuit fault. The equipment fuse should blow first if it is correctly chosen for correct selectivity (discrimination) with the upstream protection.

Fuses are not very precise devices, and they can't be individually tested, so a rule-of-thumb of simply using twice the rating for 230V for 120V is not unreasonable.

As this would take most equipment fuses used on 120V, to a range where they would be less likely to discriminate with the plug fuse and it's not needed on US standard circuits, it probably best to eliminate the plug fuse.

PMM

[emeritus]

AFAIR the requirement in the UK for new equipment to be fitted with a plug arose in the mid-1970's at around the time that the UK adopted the international harmonised wiring colours (L N E = Brown, Blue, Green or Yellow/Green stripe) instead of the UK's previous Red Back and Green colours. In the 1970's there were still large numbers of installations using the older unfused 2A, 5A and 15A installations, and it was common for appliances' instruction leaflets to mention the new colour coding for the benefit of those who might need to replace the 13A plug with a different type. Even today there must be many older houses which do not use 13A plugs, and sockets and unfused plugs to the older 2A, 5A and 15A gauges are still manufactured and readily available.

I see that 1" x 1/4" fuses are available in the US from McMaster-Carr, but only as fast-acting glass fuses, the highest rating being 8A. They are said to be suitable for up to 250V and are UL rated, but might not be suitable for equipment that has a high inrush current.

[Goodizzy]

Thank you all for the replies and education. It never ceases to amaze me the wealth of knowledge that resides here!