Electric Shower Pull Cord Burnt Out. Why?

1) Common Causes of a Burnt-Out Shower Switch

There are a number of reasons why a shower switch will burn out. These devices are not meant to last forever and as shower circuits are generally very powerful and place a lot of demand on the electrical system, the shower isolation switch can be the weak point in shower circuits. Typical reasons for failure include:

1.1) Loose Connection

Due to tiny vibrations in supply frequency, the movement that can occur in cables through using the pull cord to turn the shower on and off and expansion and contraction of different metals with heat and use of the shower, loose connections can easily develop.

Where a loose connection develops, so does a high resistance. Loose connections mean that electrical contact area is reduced and therefore resistance is increased at the connection point. Terminal connections on a pull cord can become loose over time and when a loose wire occurs, there is usually a burning smell that accompanies this on shower circuits.

1.2) Worn Out Switch

A shower pull cord switch should not be operated regularly. Their meaning is often understood and it helps to understand what these switches are actually for to understand their intended operation. A shower pull cord is a means of electrical isolation for the shower and NOT intended as an on / off switch to be used regularly. When these switches are used often, they will wear out. When they are used to turn the shower off and on whilst it is running, they will burn out very quickly! If you find that your SHOWER SWITCH BURN OUT then consider the manner in which you have been using the switch.

1.3) Pull Cord Switch Underrated

Where the shower is very powerful, the shower isolator switch needs to be rated at the same or greater level. A 50-amp electrical shower requires a 50-amp shower isolator. A qualified electrician will be able to check all these things out for you to ensure that everything is correctly rated for the load.

1.4) Shower Too Powerful

Where a shower is too powerful for the cable or shower isolator switch, there will likely be issues with overheating and burning out of the shower switch. When swapping an electric shower, care should be taken to check the rating of the new shower, the cables capacity to supply the power to the shower and the rating of the circuit breaker to ensure that the electrical load does not exceed its capacity. The circuit breaker may trip if there are discrepancies between the power of the shower and rating of the switch.

1.5) Circuit Breaker Incorrect

Where a circuit breaker is too weak to provide power to the shower, it may not trip immediately or at all. You see, a 32-amp circuit breaker will not trip when 33 amps of electrical current is demanded. Instead, the circuit breaker is likely to get warm or hot and begin to melt. Heat can travel down a cable and bust out at a weak point like electric shower switches.

2) Signs Your Shower Switch Is Failing

It is not always obvious when shower pull cord switches are failing. Everything will appear to work very well up until its point of complete destruction! There are however some signs that the shower switch may be failing if you know what to look for. 

• Loose feeling operation
• Poor Connection
• Signs of damage

Where the shower isolator switch has a loose feel to it, there may be loose connections inside the switch meaning very little resistance to switching on and off. A poor connection may mean intermittent operation of the shower and signs of damage include cracking, discolouration and burning smells! Where there are outward visible signs of damage, this usually means there is worse damage behind the scenes.

3) Steps to Replace a Burnt-Out Shower Switch

I would always advise contacting an electrician to replace electrical accessories correctly however, in some cases, minor repairs can be tackled with the right equipment.  When replacing a burnt-out shower switch and electrician follows several steps:

3.1) Isolate the electrical supply

When replacing an electrical outlet, faulty switch or shower pull cord, it is essential to safely isolate the supply. Safe isolation procedures should be followed when doing so. Once the supply has been proved dead using an approved voltage indicator and all necessary measure have been taken to prevent the re-energisation of the supply the next step can be taken.

Photo: Isolate the electrical supply safely)

3.2) Remove the old switch

When removing a damaged shower pull cord switch, it is common to find that the wiring is burnt out along with the switch itself. In many cases the wiring will be melted to the switch meaning that the wires will need to be cut in order to remove the switch fully. The wiring should be examined to determine the extent of any damage. Where the wires have melted there is a good chance that the damage will extend several inches beyond the visible damage. 

Wiring needs to be cut back to clean bright copper but this may mean there is not enough length on the cable to carry out the repair.

3.3) Install the new switch

If there is not sufficient length to safely install the new switch, the cable will need to be safely extended and joined to allow the installation of the new switch. Where joins in the cable are made, it is vital that such connections are accessible for future access, testing and repair.

I always choose a switch that matches the old one so that terminals line up correctly with the wiring. 6mm and 10mm cables can be particularly difficult to manipulate into position and anything that can make the installation easier is a bonus. 

The new terminals should be tightened so that cables cannot be wiggled out and are unlikely to fall out when the switch is screwed back into position. Cable should not be able to be trapped, crushed or damaged by the insertion of the screws.

3.4) Test at the shower

Using a calibrated multifunction tester, a resistance test should be carried out at the terminals of the shower unit itself. We are measuring continuity from the fuse box to the shower terminals of each conductor. A 6 mm cable or 10 mm cable should provide very little resistance across all conductors when installed correctly with typical values around 0.06 Ohms for the Line and Neutral conductors and around 0.10 Ohms for the Circuit Protective Conductor.

(Photo: Electrical Test Equipment for Testing Resistances and more)

Resistance values will be lower for shorter circuits and thicker cables but I always check the measured values against the estimated length of run to ensure they are correct. 

There are various test methods for checking continuity which can be found in the IET Guidance Note 3 but the test should be considered a vital part of replacing electrical accessories like a shower pull cord.

4) Preventing Future Shower Switch Failures

Leave the shower pull cord switch in the ON position. I will always advise my customers to leave this device turned on and only turn off when power isolation is necessary. NEVER use the shower pull cord to turn the shower off when it is running and avoid excessive use of the pull cord. These devices generally fail through wear and tear as a result of incorrect operation. 

Where your SHOWER SWITCH BURNT OUT if could be because of poor previous installation as well as poor operation.

5) When to Call a Professional Electrician

​If you have no knowledge of electrical testing, circuit resistances and expected values, correct torque application to electrical terminals or electrical wiring in general then ALWAYS contact an experienced electrician to carry out this work. There is also a good chance that you will not have the correct electrical test equipment to carry out the necessary safety checks on the circuit. Not only is the equipment rather expensive but it also requires extensive training to understand its use and results.

6) Understanding the Importance of Electrical Safety in Bathrooms

A room containing a bath or shower is considered a special location under the wiring regulations BS7671. This means that extra precautions should be taken in these environments due to the increased possibility of electrical shock. When our bodies are wet, the body resistance is lower meaning that the voltage can push a larger electrical current through us in the event of an electrical fault.

Most electrical work in bathrooms is notifiable work meaning that it must be notified to the local authority building control department. Replacing accessories is normally ok as long as safe isolation, testing and inspection procedures are followed.

The use of RCD (Residual Current Devices) or GFCI (Ground Fault Current interrupters) devices are vital in environments containing a bath or a shower. The requirements for these devices are set out in the wiring regulations or local electrical codes for your area.

7) What to Do If Your Shower Switch Smells Like Burning

If there is a fishy burning smell from the shower then it’s a big deal! This kind of smell indicates that there is serious damage to the cables and pull chord switch. I would always recommend an electrician tackles this repair. 

If you notice this kind of smell from the shower switch or any electrical equipment in the house then you should immediately turn off the electrical supply to the affected area or the whole house if necessary. 

This is considered an electrical emergency, as such, you should contact an emergency electrician to locate the problem and carry out repairs. If there is smoke then take appropriate action, call the fire service, and stay away from the area.

8) Summary

If your SHOWER SWITCH BURNT OUT then the right electrician should be called to deal with the problem. Your electrician will assess the power of your shower, the rating and capacity of the electrical cable and the manner in which it has been installed. Replacing a damaged shower pull cord involves electrical knowledge, specialised test equipment and experience and is not normally a job for the average DIY person. There are various reasons for a shower switch burning out and some checks should be carried out before replacement to ensure that the same situation will not reoccur.