We are regularly called in to analyse the loadings/harmonics of an installation. This may be due to intermittent tripping, excessive energy bills or premature failure of appliances and equipment. Often the overload is a result poor design with too much plant loaded onto a single circuit. It may also highlight failures in equipment to switch off at the appropriate time or even excessive supplies from the DNO.
A survey is usually carried out over a period of days to encompass peak usage and down time. A sample of recent surveys is given below
Issue: Constant Tripping at peak times
Survey carried out over a 48-hour period to assess balance of
3-phase electrical supply.
The survey showed a significant imbalance across the 3 phases with particular disparity between L1 & L3.
Maximum demand on L3 went as high as 142.8A, L1 peaked at 52.3A but was significantly lower than the other 2 phases for the duration of testing. L2 peaked at 117.5A.
The incoming supply has 100A fuse carriers, however these need to be checked to ensure rating. 100A fuses will cope with these high loading for a considerable amount of time but 60A & 80A fuses will fail in
approximately 8.5 mins & 50 mins respectively. This would cause considerable disruption to the businesswith all 3-phase equipment and all single-phase equipment on L3 failing.
Whilst 100A fuses will cope with the overload experienced this situation needs to be addressed as undue stress is being placed upon the installation.
It is recommended that further investigation is carried out to identify suitable single-phase circuits on L3 to be migrated across to L1. L2 circuits may also be suitable to move in order to achieve a uniform balance.
Issue: Intermittent Tripping at peak times
Survey carried out over a 24-hour period to assess the loading on servery socket outlets due to persistent tripping at peak load time.
A maximum reading of 27 Amps was recorded. The circuit was protected by a 32A MCB. Whilst the reading was at the higher end of the rating this was perfectly fine and no tripping should be experienced at this level.
Further investigation highlighted that portable equipment had been moved to other circuits leading to high demand in certain areas with the recommendation for additional circuits to be added from the distribution board during the upcoming refurbishment works.
Because a 32A Type B MCB requires an overload of 50 amps to trip within 17 minutes a significant overload had
been regularly occurring and this needed addressing as soon as possible.
Issue: Power Surge Leading to Failure of Installations in places
All remedial works following over voltage have now been completed. Building is now working correctly.
A Power analysis survey has been completed with no inherent issues recorded relating to power problems. It is our belief that a connection failure was the sole cause.
There were however recorded events of high supply voltage. Supply voltages should be within 10% of nominal voltage (230V), recordings of 253.4 &253.5 were recorded. This will shorten the life of electrical equipment over time and result in higher electricity charges. This is a matter for the school to address directly with their utility supplier.