How to Choose the Right Wires and Circuit Breaker for Heating Film Installation

Hello, this is Jay Lee from Hi Heat.

In this article, I would like to explain two very important points that are
often overlooked during heating film installation:
how to choose the correct electrical wires and
how to select the proper circuit breaker.

A typical heating film installation process includes laying insulation,
installing the heating film, and then connecting the electrical wiring.
The choice of wiring at this stage has a direct impact on safety,
reliability, and long-term durability.

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1. Always use stranded wire, not solid wire

The most important rule when selecting electrical wire is to use
stranded wire, not solid wire.

Stranded wire consists of multiple thin copper strands bundled together,
while solid wire has a single solid copper core.

Electricians are usually familiar with this difference, but many end users
are not, and solid wire is sometimes used by mistake.

For heating film installations, stranded wire should always be used.

2. Why is solid wire dangerous in this application?

If you look at the back of a thermostat, you will see screw terminals where
the power supply wire and the heating film wire are connected.

When a solid wire is inserted into this terminal and tightened, the screw
often reaches a point where it cannot be tightened any further.

As a result, the contact area between the copper wire and the terminal
becomes very small.

This situation is similar to a traffic bottleneck: when current flows
through a very small contact area, resistance increases and heat is
generated at that point.

In real installations, this heat can transfer all the way to the front
panel of the thermostat, causing the plastic housing to slowly deform or
melt. (This is based on actual field experience.)

Over time, the thermostat can become damaged, and in the worst case,
this can lead to a fire.
That is why solid wire should never be used in heating film installations.

3. What makes stranded wire safer?

When stranded wire is inserted into a terminal and tightened, the individual
copper strands spread out and make contact over a much larger surface area.

A larger contact area allows current to flow smoothly and prevents
localized overheating.

For this reason, we strongly recommend using
stranded wire together with proper terminals
when connecting wires to thermostats and when connecting wires to the
heating film.

When crimping or tightening terminals, do not do it lightly.
Apply firm pressure so that the wire and terminal are securely bonded.

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4. A wiring method that must be avoided

At a trade exhibition, I once encountered a very dangerous wiring method
being used.

The installer explained that he inserted the wire between the copper busbar
and the silver layer of the heating film and then fixed it with butyl tape.

At first glance, this may appear to work, and some people claim they have
never experienced a failure using this method.

However, the wire is not mechanically secured inside the film, which means
even slight movement can cause arcing and sparking.
This is extremely dangerous.

If no failure has occurred yet, it is more likely that the problem simply
has not been noticed.

Always use proper terminals, and always crimp or tighten them firmly.

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5. Wire thickness is like road width

Wire thickness can be compared to the width of a road.

A wide road allows many cars to pass smoothly, while a narrow road causes
traffic congestion.
Electrical current behaves in the same way.

If the wire is too thin for the required current, heat will be generated
as the current flows.

As the wire insulation repeatedly heats up and cools down, it can harden,
crack, and eventually expose the conductor.

Once insulation cracks, exposed wires can touch each other and cause
sparking, which may lead to a fire.

The classic movie The Towering Inferno famously showed how
undersized wiring can cause catastrophic fires in buildings.

6. Example: selecting a circuit breaker and wire size

Let us assume that the total installed heating film power is 5 kW.

Current can be calculated using the following formula:

W = I × V → I = W ÷ V

5,000 W ÷ 220 V = approximately 22.7 A

The circuit breaker must be rated higher than the required current,
so a 30 A circuit breaker would be appropriate.

If a 20 A breaker is used instead, the power will trip immediately when
the heating film is turned on, even if there is no leakage current.

Once a 30 A breaker is selected, the wire must have an allowable current
rating higher than that value.

In Korea, a 4 sq mm stranded wire (approximately 35 A) is
commonly used.
In AWG terms, this corresponds to approximately AWG 11.

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Summary

To summarize the selection process:

① Calculate the required current (A) based on the total heating film power

② Choose a circuit breaker with a rating higher than that current

③ Select a wire with an allowable current higher than the circuit breaker

For users who are not familiar with electrical work, we do not recommend
installing heating film over large areas on your own.

If a large installation is required, always use a professional installer.

Even for small installations, always verify wire capacity and circuit
breaker ratings before installation.

The video below explains the same content with real installation examples.
We strongly recommend watching it together with this guide.

▶ Watch the related video: