20-03-2014, 11:58 AM
I've had to consider this question of fusing & mains wiring many times over the years, when renovating comms. receivers. My approach is as follows (with the rare, occasional exception *) - assuming an a.c. mains only set with a centre-tapped secondary winding on the mains transformer.
1. Route the incoming mains to a suitably-rated DPDT switch first (* the RCA AR88D / LF is a classic exception here) - and then fit a fuse (typically 2-amp. anti-surge) in the "L" feed from that switch to the transformer primary. (Yes, I am aware that there are two schools of thought on this: which comes first: the switch or the fuse? There are pros and cons in either approach.)
2. Fit a fuse between the centre-tap of the transformer secondary to chassis (which is usually the 0v. point). Something like 100 mA to 250 mA anti-surge is usually adequate.
3. All soldered joints, connections and tags that are carrying mains voltages are well-insulated with heat-shrink sleeving.
4. Fit a conventional 3-pin mains plug with a fuse of appropriate rating: usually 3-amp.
5. Always use 3-core mains cable, suitably rated, with the earth wire securely bonded to the receiver's metalwork. Ensure that that cable is mechanically secure to the chassis.
Such changes do indeed sometimes change the originality of a set, but that is a change that I consider worthwhile on the grounds of safety: safety for the set, the set operator and set maintainer. (I speak from personal experience in the last category: ouch!)
Al. / Skywave / March 20, 2014.
1. Route the incoming mains to a suitably-rated DPDT switch first (* the RCA AR88D / LF is a classic exception here) - and then fit a fuse (typically 2-amp. anti-surge) in the "L" feed from that switch to the transformer primary. (Yes, I am aware that there are two schools of thought on this: which comes first: the switch or the fuse? There are pros and cons in either approach.)
2. Fit a fuse between the centre-tap of the transformer secondary to chassis (which is usually the 0v. point). Something like 100 mA to 250 mA anti-surge is usually adequate.
3. All soldered joints, connections and tags that are carrying mains voltages are well-insulated with heat-shrink sleeving.
4. Fit a conventional 3-pin mains plug with a fuse of appropriate rating: usually 3-amp.
5. Always use 3-core mains cable, suitably rated, with the earth wire securely bonded to the receiver's metalwork. Ensure that that cable is mechanically secure to the chassis.
Such changes do indeed sometimes change the originality of a set, but that is a change that I consider worthwhile on the grounds of safety: safety for the set, the set operator and set maintainer. (I speak from personal experience in the last category: ouch!)
Al. / Skywave / March 20, 2014.
