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One thing to raise with whoever checks the work: the condition of the wiring itself.

Houses old enough to have no ground often also have insulation that has become brittle, and connections that have been worked on repeatedly over decades. An interrupter protects against a fault to earth; it does nothing about deteriorating insulation between conductors or a loose connection heating up in a box.

So the outlet upgrade is a real improvement and it is not an assessment of the system behind it. Worth having somebody look at a couple of boxes while they are there.

If you genuinely cannot avoid one, the version that is least bad:

• Heavy gauge, short, and rated above the heater's draw with margin.
• Fully uncoiled, laid out where nothing covers it.
• Nothing else on the same circuit, and check what else is on that breaker.
• Feel the plug and the cord after twenty minutes. Warm is a warning; hot means stop.

But the better answer is usually one of: use a heater on a circuit that reaches, have an outlet installed where you need it, or use a different heating method for that spot. An added outlet is a small job and it removes the problem permanently.

Since you have no meter to hand, there is a classic improvised test that genuinely works for low-voltage DC: use a potato, or a glass of salty water.

With the supply unplugged, cut and strip the two conductors and separate them well. Push the two bare ends into a potato a couple of centimetres apart, or into a glass of salted water without letting them touch. Then power the supply.

Electrolysis produces visible bubbling and, in a potato, a greenish discolouration. The bubbling is more vigorous at the negative conductor, and in a potato the corrosion mark appears at the positive one.

It is crude, it is slow, and it is a real technique that predates cheap meters. Keep it to genuinely low voltage DC, use small currents, and wash the potato off your hands afterwards.

Having said all that: buy the meter. You will use it for the rest of your life and it removes this entire category of question.

To be concrete about the sequence:

1. Do not touch the nail or anything attached to it.
2. Go to the panel and switch off the breaker for that circuit. If you cannot identify which one, switch off the main.
3. Confirm the circuit is dead — the lights that flickered should not come on with their switch.
4. Put a note on the breaker so it stays off.
5. Leave the nail where it is and call an electrician. Removing it does not help and disturbing it can make the damage worse or leave a live conductor exposed inside the wall.

If the circuit that went dark also feeds something you need — a fridge, a medical device — run an extension from a different circuit rather than switching it back on.

It is worth adding that pulling is not as hard as people fear, and the reason the rule survives is partly that the correct method is genuinely easy once you have done it.

Fish tape or a pull string left in during assembly, proper pulling lubricant, and a second person feeding at the far end. A long run with several bends needs an intermediate pull point, and the codes limit how many bends you may have between access points for exactly this reason.

If a run is so difficult to pull that assembling around the wire seems attractive, that is usually a signal that the run needs a pull box in the middle rather than a different technique.

The solvent for that family of adhesives is acetone, and the most available source in a house is nail polish remover — check the label says it contains acetone, because many are sold acetone-free and those will not work.

Method:

1. Soak the joined area in warm soapy water first for a few minutes. This softens skin and sometimes gets you most of the way.
2. Apply acetone to the bond line with a cotton pad and keep it wet against the join for several minutes. It needs contact time; wiping it on does nothing.
3. Roll or peel the fingers apart sideways, slowly. Do not pull them straight apart.

The rolling motion matters. Cyanoacrylate is strong in tension and weak in shear, so a sideways peel separates it at a fraction of the force a direct pull needs — and a direct pull is how people tear skin.