In recent years with the increase in communication system and telecommunications, the photovoltaic (PV) sector and the mature railway sector have seen a dramatic increase in the requirement to monitor, measure and meter DC systems and in the case of PV and Railways at high voltage potentials.

Foxtam Controls have particular expertise in providing monitoring and measurement solutions for the DC market, including high potential systems gained over many years in supplying equipment to the railway sector.


tube train

Traction Voltage

The railway sector, particularly those that utilise “conductor rail DC traction voltage”, such as the London Underground, have used our voltage sensing relays (YWRU), available in several voltages up to a DC potential of 1500VDC to monitor the status of traction supplies. These voltage transducers have also been used with a measuring range up to 1000VDC to facilitate a continuous status output via an analogue mA signal, (FOX.TR.DU).

A recent railway application involved monitoring conductor rail heaters, prevent icing, icing can cause locomotive traction supply loss. The nominal-traction-voltage is 750VDC and all equipment must have a permanent capability up to 1000VDC, wide fluctuations are not unusual.  Often, with higher potential DC systems the only supply available is the fluctuating DC potential, similar to the PV market.  The majority of monitoring and measurement equipment requires a stable DC auxiliary supply.  We stock a range of DIN rail mounted DC to DC converters ranging from 9-36VDC to 210-1200VDC with a choice of secondary voltages: 5VDC, 12VDC and 24VDC to power equipment or to provide an analogue loop supply.

dc system monitoring devices
YWRU Series Voltage Control Relays

Another consideration in DC monitoring and measurement is obtaining a current reference which occurs with the conductor rail heaters application, heater called for means current pulled, no current equals element failure or supply fault. Traditionally, DC shunts have been utilised that are not economical in size for higher currents making them difficult to install as well. Safety is important due to the high voltage potentials the applications have and isolation between the primary current and the mV secondary attributes is something DC shunts also lack.

DC Monitoring and Metering

Foxtam Controls offers a wide range of “DC CT's” including split cores. These are Current Transducers providing a fully isolated analogue DC voltage signal output or a mA output, including 4-20mA loop-powered options.  Available current ranges are from 50 Amps to 30,000 Amps.

In the conductor rail heaters application, DC energy metering (KWh) was required, the “DC CT's” also provided the current input reference to our DC multi-parameter display energy meter, (VAW) a DIN 96x48mm panel mount displaying DC Volts, Current,  Watts and KWh.  The VAW can be specified for any input voltage range up to 1000VDC and the current input reference can be specified for an mV secondary shunt or any analogue signal from a “DC CT” transducer along with the primary current range.  The VAW meter can be utilised as a display only meter or can be specified with alarm relay set-points, analogue outputs, RS485 MODBUS or a combination.

dc system monitoring build

The VAW meter has also been utilised within the telecommunications sector, whilst the supply potential is not as challenging, generally 48VDC nominal battery-backed floating at 54VDC the applications have often been retrofitted on a 24/7 system.  Again, our split core “DC CT's” suited the application perfectly along with our DC to DC converters proving a stable auxiliary supply voltage for the CT's and the VAW meter.

dc system monitoring
YWRI.DEF and VAW Panel Meter

Earth Fault Monitoring

Some DC systems are Earthed, and it’s not unusual for them to be floating and the rise in DC applications has increased the need for DC Earth Fault Monitoring Relays.  We have the answer with our DC Earth Fault monitoring solution (YWRI.DEF) coupled with a DC CT (FOX21.CTD).  The YWRI.DEF has all the attributes of its AC system brother, adjustable sensitivity and delay timers, test input and selectable via the latch function to be “auto” or “manual” reset, and is suitable for use on Earthed or Floating Systems. With an Earthed System, the CT is placed only on the earthed conductor, on a Floating System both the positive and negative conductor passes through the CT.  The YWRI.DEF has a common relay output indication that will advise if the earth fault is in the positive or negative conductor.

Foxtam Controls has a wide scope of experience in providing DC monitoring, measurement and metering solutions to a multitude of industrial and commercial applications. We look forward to assisting you with your next challenge so call us on +44 (0) 161 6265316 or email us at to discuss your requirements.