Why not use normal safety boots?
- Electric current can jump (arc) over 40mm at 5000 Volts
- The sole of a normal safety or boot or shoe is typically less than 10mm thick and is made of anti-static material that is not electrically insulating
- The upper of safety boots when wet or damp will conduct electricity - This includes such materials as waterproof leather as the waterproof coating is thin and can be easily damaged
- Perspiration can make the leather damp enough to fail an EN 50321 test
- This is why EN 50321 specifies the height of the boot or shoe and that the foot should be enclosed by the footwear
Dielectric boots vs protective matting
Electrically insulating footwear provides just one part of your personal protective equipment. Dielectric boots should be used, where possible, in conjunction with electrically insulating gloves, tools and matting. Dielectric gloves share the same classes as the boots in EN 53021-1:2018. Gloves are often your first point of contact with potentially dangerous high voltage equipment.
Dielectrc matting is often used in areas to cover live or potentially dangerous parts. However dielectric matting has its limitations. It is often very heavy therefore moving it around can be strenuous and increases the risk of the worker not using the equipment. It can also be easy to accidentally step off an electrically insulating matt, especially if there is a risk of something falling from above. Dielectric footwear provides full freedom of movement for the operator, rather than being restricted to the area of the insulating matt. For this reason dielectric footwear should always be used when you are using dielectric matting, providing an extra layer of protection through redundancy.
The bright yellow and green compounds of dielectric footwear is highly viasble and therefore makes it clear to a site manager that the PPE is being worn.
Where are they used?
- Power generation and distribution (e.g. Western Power, EDF and National Grid)
- Electrified transport systems such as the Railways
- Utility companies who run the risk of cutting electric cables whilst digging or moling
- Power sub-stations were the current can jump distances (e.g. Hospitals and Shipping)
- Wind Farms
- Dielectric boots should be used with a second barrier in case one barrier fails, typically a dielectric glove.
Manufacturers must test every piece of dielectric footwear to EN 50321-1:2018. The test involves filling the boot with water and submerging it in a water bath, an electrode is placed inside the boot, with a second electrode connected to the metal frame of the bath. A test voltage is then applied. Boots are tested at the appropriate leakage current test voltage for their class rating (see table below) for three minutes during which the leakage current must not exceed the maximum permitted value for the class rating. For certification, boots are tested to the withstand test voltage, but this is considered a destructive test.
Workmaster™ test all of their boot and overboots with alternating current (AC) as standard, but Direct Current (DC) testing is available on request.
|Class Rating||Maximum Working Voltage||Withstand Test Voltage||Leakage Current Test Voltage||Maximum Leakage Current|
|Class 0||1kV||10kV||5kV||5mA (8mA)|
|Class 1||7.5kV||20kV||10kV||10mA (16mA)|
Workmaster Dielectric Automatic Test Machine
Re-testing dielectric footwear
Not many people are aware that Annex B2 of the standard for dielectric footwear - EN 50321-1:2018 (Electrically insulating footwear for working on low voltage installations), requires that all approved dielectric footwear is re-tested every year.
Every pair of dielectric boots is tested to the methods in the EN 50321 standard during manufacture. Part of this test method, the ‘Proof Voltage Test’ should be performed annually (or at the interval defined in local national standards if this is different), once the boots are in service, along with a thorough visual inspection of the boots.
A Proof Voltage Test requires that the boot be filled with water to within 4cm of the top of the boot and that it is submerged in a tank of tap water to the same level. A probe is placed inside the boot and the circuit is completed through an earthed electrode in the water tank. For a routine Class 0 test, a voltage of 5kV is applied for three minutes and the current passing through the probe must be less than 5mA for a moulded boot.
This is why Workmaster™ boots have a space to record periodic inspection testing next to the CE markings on the boot. This requirement applies to all CE marked dielectric footwear from every manufacturer - if boots are not re-tested then they are effectively no-longer compliant to the standard.
Care of Insulating Boots
Boots should be rinsed off after use, especially if they have been in contact with aggressive chemicals or any other type of contaminant. If the insulating footwear in not cleaned regularly after use then damage may occur if chemicals are not removed from the boot.
The boots inner lining should be cleaned periodically with a mild detergent and the insoles on Workmaster™ boots can also be removed and are machine washable.
Dieletric footwear should be checked prior to use. It is important to visually inspect the boots for any defects such as cuts as a damaged boot may not give the specified level of protection, putting the user at risk. Damaged boots should be replaced.
When the soles are inspected if yellow can be seen anywhere except for the 6 mm circle in the centre of the heel of the blue rubber sole then the Dielectric boot should be replaced.