110 Volt vs 240 Volt on Construction Sites

Sunrise Tools provide various angle grinders, electric drills, dust extractors and mixers for a range of applications in the Construction and Maintenance sectors, all for single phase supply with almost 75% delivered in 110 volt. Whether this indicates an appreciation of the safety benefits of the lower operating voltage, we are not always sure. We think it wise to use the lower voltage products wherever possible. Below we have provided an insight into these matters, based upon typical conversations with callers to our business: 


Q. Why do we have 110 volt site working in the UK and Ireland?

A.         Because it is considered to be safer than 240 volt working

The hazardous voltage you are exposed to in a 110 volt system is actually only 55 volt. By comparison, a direct mains connection is nominally 230 volt. You are more likely, by a considerable margin, to survive a 55 voltshock, than one at 230. 110 volt supply is described as Centre Tapped to Earth (CTE) and comprises minus 55 and plus 55 volt circuits, hence the 110 volt Potential Difference, also known as Voltage

Q. Surely an RCD on the 240 volt supply will protect me?

A.         It is a good solution, but NOT perfect

An RCD (Residual Current Device) should quickly break the circuit if a current leakage to earth is detected. However, the weakness with an RCD is that it is an electro-mechanical device and has the potential to fail. If the latter happens, you have little  protection from the full 230 volt shock. 

Q. Is it a legal requirement to use 110 volt?

A.         Not that we know of, but it is widely accepted Best Practice

Employers and Site Operators have a significant obligation to ensure persons engaged on their behalf are not exposed to undue risks. The default for operation of single phase electrical equipment on site has therefore become 110 volt, as it is generally accepted as being inherently safer. This permits the Employer / Site Operator to most effectively discharge their responsibilities to persons under their control. It will be rare to find a Commercial Construction Site that permits 240 volt working. 

Q. What size of 110 volt transformer do I need?

A.         You simply add up the requirements of the devices being connected and …

It is almost that simple but there are some important considerations to bear in mind. There are three popular sizes of 110 volt portable transformer, 3 kVa, 3.3 kVA and 5 kVa. As an approximation, these will support loadings of 3, 3.3 and 5 kW respectively. So add up the wattage of each connected device (should be shown on the equipment label) and make your selection. BUT TAKE NOTE - portable transformers will typically only deliver their maximum output for about 5 minutes. If your application involves longer running, you have to assume power output from the transformer will be reduced by 50%. The CONTINUOUS ratings (more than 5 minutes continuous operation) for the three transformers previously listed are 1.5, 1.5 and 2.5 kW

Q. With 110 volt, what length extension cables can I use?

A.         One 15 metre extension cable of the CORRECT construction …..

Because of the reduced voltage level, 110 volt tools operate with double the current (amperage) of 240 volt equivalents. This means cables with larger copper cores (larger cross section area / csa) are needed. The thinnest 110 volt cables (1.5 mm² csa) are only suitable for light loads such as lighting or single power tools. A load of greater than 800 watt needs a minimum 2.5 mm² csa cable. Using a larger core cable is rarely a handicap, hence for maximum efficiency, the 4 mm² csa variety should be used wherever possible. Only one 15 metre extension cable should be used between the transformer output and the power tool – if you use excessively long 110 volt extension cables, you will experience significant voltage drop. This will cause increased current flow which will potentially overheat and damage both the cable and attached electrical devices.

Power supply issues can afflict both 110 and 240 volt working. If you’re operating in a domestic, office or small site situation, where the power source is the standard ring main, you’re likely to make connection through a 3 pin plug fitted with a 13 amp safety fuse; that alone will limit you to supporting approximately 3000 watts of equipment.

An established construction site is likely to have site distribution boxes, fed from a 400 volt, 3 phase supply. For single phase working, you should expect to get a reliable 16 amp on the 240 volt outlets, 32 amp on the 110’s. These should support a slightly higher loading, circa 3600 watt.

The performance of battery-operated power tools continues to improve but they are still some way off supporting the requirements for continuous high energy working that many corded power tools are required to deliver. By a strange coincidence, the latest breed of batteries deliver 55 volt.

If we can provide further assistance in these matters, do call us on 01794 830 841 or email enquiries@sunrisetools.co.uk . If you feel anything about this article is incorrect or misleading, do email or phone us and we’ll consider any revisions you suggest.

Sunrise Tools - November 2016

Posted in: Sunrise Updates