Double Pole Fuses - Fused Neutral

Problems that fused neutrals can cause, and why they exist in the first place.
Fused neutrals have not been permitted in the UK since 1955.

[@kibi15]

The house that I grew up in had a 3 phase supply, with a fused neutral. When this neutral fuse failed one day, it had the effect of connecting various light loads in series with heavier loads across any two phases. The light loads had a higher voltage drop across them and the heavier loads less voltage than usual.

[@CrazySparkie63]

Hi John, although you say NOT permitted since 1955 there were exceptions, when I was a kid back in 1967 we finally got Leccy installed, the supply was 200v ac 50hz (or cycles per second back then) CTE so we did have a neutral fuse. I still have the inventory and my Cousin (who worked for the DNO) installed the service cable and head) I later found out that the supply came from Fulham Broadway Tube station. We went back to the Gas lights.

[@nemthefearless]

Superbly deadpan as always. Reminds me of those old Open University documentaries from the 80s, or the exquisite "secret life of machines" series. None of this faux hipster nonsense!

[@elliep71]

Very informative video, thank you. I had no idea! I moved into my old 1920s house 5 years ago. The whole house had been rewired and had a modern fusebox before I moved in. It was only when I had an electrician come to install something that he mentioned I had a fused neutral and to contact the National Grid. They replaced the old cast iron box earlier today! I have a TT earthing arrangement, common in older houses and because of this the reading on the installers multifunction tool was too high and they refused to wire the induction and advised me to get an electrician, which ended up being beneficial to me. I'm surprised, i've had electricians in before for other things and it had never been mentioned until recently...some 70 odd years since the legislation changed!

[@intelmacs]

Split phase is still common in rural areas of the UK, with 480v between phases and 240 phase - neutral.

[@BenjaminEsposti]

Hah, that's like the split system here in the USA. We have two lives and a neutral coming into our houses. That way we can get 120V, or 240V for bigger, more power hungry appliances. The 240V hookups are what we refer to as "douple-pole", when talking about circuit protection. Two circuitbreakers are sitting next to each other, with a link on the handles to join the two. If one of them trips, then they both will trip to the off position. I just finished helping my father the other day, we changed and added some circuits in his kitchen, as he is remodeling it.

[@juhanasiren6824]

An example of a double sided DC supply is the London Underground traction current, which has the centre rail at -210 V and the outside rail at +420 V, giving a total supply voltage of 630 V.

[@paulneedham5900]

Thanks John, excellent explanation.

[@TonyP9279]

I have seen "neutral" fuses in catalogs but never really knew what used them. These were solid shunts (can't be blown) so I figured there were some places where this were useful. I live across the pond in the land of center-tapped transformers so I have never seen a neutral fuse, at least in an unrigged circuit.

[@davemccomb8683]

Excellent video, just found out we had a fused neutral, when the Engineer said he cannot convert to a smart meter whilst it was there. Now I understand why. He still could have swapped the damn thing out but 'apparently' that's not HIS job.......

[@jwflame]

Metering is now totally separate from the supply equipment, although in the past it was not.

[@ve2zzz]

I once had to service an audio power amplifier. The good part was that the trouble was easy to find: A blown ground connection. The bad part was that ALL of the semiconductors were blown and many electrolytics had exploded. For me,it is clear: You NEVER fuse a neutral or an earth connection.

[@jrmcferren]

In the US our neutral is on the Center tap, but prior to the 1928(?) code, even that was fused, in installations with both sides of the line (our AC center tap system was devised from a DC system with a center tap at the generator) you would have fuses in both lines and neutral. In many homes we didn't get 240 until after WWII when electric ranges (I think you call them a cooker over there, but I'm talking combined oven and cooktop).

[@ernstpeterlegrand]

Wow, I have a double fuse. Makes all sense. Could also replace it with a double pole breaker as that would whatever happens break both? Correct, and then place a surge protection next to it in the same box.

[@skabbymuff111]

Thanks for this explanation

[@johnschlesinger2009]

In this fusing arrangement, the neutral often blows first, possibly because when mains electricity was first used, they got the direction of electron flow wrong.

[@dimitrisblane6368]

thanks for your videos. They are very informative! Can you explain what the difference is between a single pole C32 MCB and a double pole C32 MCB. What's the benefit of having a double pole MCB?

[@zanimljivastruja7511]

I have seen that someone connected neutral conductor to switch and what happens is that when LED lamp is turned off it glows.

[@jagardina]

The 240v household circuits in the US have breakers that will shut both rails when either one is tripped.

[@TechHowden]

no

[@jrmcferren]

Common trip is rather new, there were some circuit breaker systems where both poles were independent just like the fuse boxes. These panels and their common trip equals were commonly made by Federal Pacific Electric and are prone to not tripping on a fault.

[@DIYElectronicsGeek]

In Norway we have 2-pole automatic resettable fuses... The 2 poles are mechanically connected together so either Live or Neutral may trip but both Live and Neutral will be broken. Makes sure that when the fuse trips, the circuit will be very much dead.

[@Bunchiebunchie]

+ElectroGeek Worth mentioning, most of Norway also use IT earthing systems, where you have a voltage of 230 volt between the live wires, and 133 volt (230 volt divided by √3 for 3 phase systems) between live and earth. There is no neutral wire present. In transformer circuits where a earth fault is present on one of the live wires, the potential will be the same for earth and the live wire with the earth fault , and 230 volt between earth and the other two live wires. We always install circuit breakers for all live wires, and for the 400 volt TN-C-S or TN-S earthing systems, a circuit breaker also needs to cut the neutral wire. TN systems is still uncommon in most parts of Norway, so we need install two pole switches for bathrooms, even if the neutral wire has same potential as the conductive floor.

[@paul60163]

Power station workshops can use the centre-tap earthed 55-0-55 V instead of 240 V, presumably to reduce risk of electrocution (dual-fused IEC mains inlet connectors are available, but no doubt these shouldn't be used with standard 120V or 240V mains supplies) en.wikipedia.org/wiki/Electric_shock

[@michaelcox2648]

Hi john. Can you do a video on how to wire an extractor fan with timer to fused connection unit a long with fan isolator. It seems there are no 3 pole Fcu's so how do you fuse down the switch live? Would be appreciated. Thanks again and keep up the good work. Michael C.

[@zanimljivastruja7511]

I won't be suprused if this double fuse board survived WW2.

[@aquahits5674]

Hi john can you fit fuse on phase and nuetral line so thats 2 fuses that has been advised to fit on laptopchargng cab for euro

[@jwflame]

No, neutral fuses have not been permitted since the 1950s. If you want double pole disconnection when there is a fault, fit a 2 pole circuit breaker. The only other situation where 2 fuses are used/permitted is with centre tap supplies such as the 110V used on construction sites, but in that case neither of the connections are really neutral, and even there it is more usual to have circuit breakers.

[@sumitraj609]

Hi John would you able to go through the certificates filling mate plz

[@jwflame]

kzbin.info/aero/PLVsHvs2SuqmqKOCwtYX8ap-grW9oKRs-j

[@TestECull]

Eh, if the old fusebox is still in serviceable condition, leave it be. Replace the neutral fuse with a solid link, make sure it's earthed properly, and let it be. No need to replace the entire unit when modernizing it costs pennies and can be done...more or less...by anyone.

[@djturbine7565]

Brilliant idea, advising people to open their ancient fuse boxes and begin replacing fused neutrals with solid links. Idiotic thing to comment.

[@TestECull]

@@djturbine7565 Not supposed to fuse the neutral and British plugs have a fuse in the line side. But that doesnt matter to someone trying for a comment section zinger, does it?

[@djturbine7565]

@@TestECull While it’s a simple task in an of itself, people who don’t know what they are doing, should not be going into old fuse boards to replace or touch anything. With no RCD protection and more likely than not asbestos within the old ceramic fuse carriers, they are dangerous places to start sticking your untrained fingers. Saying it “can be done by anyone” is foolish, as you know people are stupid enough to go and try it. I couldn’t care less about the zinger, I just have an issue with people giving out dangerous advice on YT.

[@DrQuadrivium]

Double pole fusing was, of course devised by highly qualified 'experts'. .