bx to non-bx

Yes as long as this splice is in a box with a cover.

The critical question is the actual nature of the present cable. Is it really BX which is a spiral metal clad cable with a paper over wrap around the conductors and no bonding strip, is it type AC armored cable with a bonding strip inside the armor, or is it type MC cable with a plastic over wrap around the conductors and an insulated green equipment grounding conductor (EGC)?

If it is really "BX" without the bonding strip then you may not extend the circuit. You would have to run a new circuit from the panel to the new receptacle outlet.

If it is type AC or MC you would extend the circuit using 10/3 wg NM and install a NEMA 14-30R receptacle. If you are changing from the three wire NEMA 10-30R receptacle you will need to remove the bonding strap or wire that connects the neutral to the dryer frame and then install a four wire dryer cord to the dryer terminals.

-- Tom

My guess is if they used bx in the first place you need to use bx to extend the old wiring. You can splice into the existing box if you can remove the cover of the existing box exposing the tap connections after the remodling is finished. The ground needs to make metal to metal contact so the screw is the perfect place for it.

It's the firs time I hear the term 'bx', but I think you should replace the whole length of cable, from the electrical box.The few more bucks you will pay are worth it.Here, we use wires of type 'H05VV-F'which means:H:Harmonized with european standards, 05:up to 50 Volts RMS, V:with a PVC jacket, second V:conductor insulation is PVC, F:conductor is made of fine copper wires.Former nomenclature is NYLHY. That bx sounds like a very old type of cable. In conductors that carry a large ampacity you should avoid such connection in boxes etc. except when necessary, because in these points there is voltage drop, loss of power and heat build-up.

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Ok, apologies if I appear dense. I believe now it's AC, but I'm going to describe the cable just to be sure, if the group will indulge it:

three copper wires wrapped in rubber (white, black, red) each wrapped in paper also a thin flat aluminum strip all this wrapped in a brittle red rubber inside a spiral metal armor.

Sound like AC or BX?

Thanks a lot

That is type AC and if made up properly the armor is suitable for grounding. If you are using the 3 prong plug you will actually have a redundant ground/neutral path. The current code requires a 4 prong plug and independent ground/neutral but there was never a body count to justify that. It was simply changed as part of a rewrite of article 250 to bring consistancy to the rules. I would say you would be safe to extend which ever practice your current setup is using. You could (and probably will) get a flame war going about whether it is safer to use a shared ground/neutral or to use the shield of the Type AC alone for grounding.

It is type AC armored cable. You can extend the circuit with any wiring method that is acceptable under the local electrical code. Since you have a fully insulated neutral and a recognized Equipment Grounding Conductor (EGC) you would be well advised to change the outlet and the dryer cord to four wire NEMA 14-30. With the existing three wire circuit if the neutral (white wire) ever develops an open the entire frame of the dryer will be energized to 120 volts. With a four wire circuit an open neutral will only stop the dryer from working. The fourth conductor will keep the frame at ground potential thus avoiding a shock or electrocution hazard. It's your home and family which one seems smarter to you.

-- Tom Horne