Soldering Old Wiring

Ravenvalor

Senior Member
Hello,

I have to make a splice onto a neutral in a junction box that has what appears to be either knob and tube or the old BX cable in it. There is hardly any conductor in the junction box to work with. I was wondering if it would be ok to solder a conductor onto this neutral conductor and if so is there a special solder that I should use?

Thank you,
 

iwire

Moderator
Staff member
Location
Massachusetts
There is no NEC section prohibiting a soldered joint, there is this.

110.14 Electrical Connections. Because of different characteristics
of dissimilar metals, devices such as pressure
terminal or pressure splicing connectors and soldering lugs
shall be identified for the material of the conductor and
shall be properly installed and used. Conductors of dissimilar
metals shall not be intermixed in a terminal or splicing
connector where physical contact occurs between dissimilar
conductors (such as copper and aluminum, copper and
copper-clad aluminum, or aluminum and copper-clad aluminum),
unless the device is identified for the purpose and
conditions of use. Materials such as solder, fluxes, inhibitors,
and compounds, where employed, shall be suitable for
the use and shall be of a type that will not adversely affect
the conductors, installation, or equipment.



(B) Splices. Conductors shall be spliced or joined with
splicing devices identified for the use or by brazing, welding,
or soldering with a fusible metal or alloy. Soldered
splices shall first be spliced or joined so as to be mechanically
and electrically secure without solder and then be
soldered.
All splices and joints and the free ends of conductors
shall be covered with an insulation equivalent to that of
the conductors or with an insulating device identified for
the purpose.
Wire connectors or splicing means installed on conductors
for direct burial shall be listed for such use.
That said, from my seat here in the living room it sounds like a really bad idea to mess with the old wiring.
 

Ravenvalor

Senior Member
There is no NEC section prohibiting a soldered joint, there is this.



That said, from my seat here in the living room it sounds like a really bad idea to mess with the old wiring.
Thank you iwire. I should have considered split bolts before soldering. I have been cleaning up a mess on another job where the former owner was an engineer who loved to solder splices. I guess my brain has solder locked into it.
 

Strathead

Senior Member
Thank you iwire. I should have considered split bolts before soldering. I have been cleaning up a mess on another job where the former owner was an engineer who loved to solder splices. I guess my brain has solder locked into it.
How did you get to split bolts from what iwire posted? The code part about the solder refers to using electrical solder not acid core plumbing solder, the part about mechanical just means, twist the wires before soldering, don't depned on the solder as the only means of connecting the conductors.

Now to your original question, you should not do either. You should locate a new J box closer to the source, and another one closer to the load, and run a romex jumer in between. Now your wires will be long enough and you don't have to worry about the integrity of the short wire and insulation.
 

kwired

Electron manager
Location
NE Nebraska
the part about mechanical just means, twist the wires before soldering, don't depned on the solder as the only means of connecting the conductors.
I think that is why he though of the split bolt - mechanically connected before soldering. Kind of hard to do if conductors are short in first place, but not necessarily impossible. That is before getting into possible issues of amount of free conductor in the box.
 
Hello,

I have to make a splice onto a neutral in a junction box that has what appears to be either knob and tube or the old BX cable in it. There is hardly any conductor in the junction box to work with. I was wondering if it would be ok to solder a conductor onto this neutral conductor and if so is there a special solder that I should use?

Thank you,
If it's K&T it should be solid wire. These are great for that:

View attachment 7023
 
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