Types of low voltage (LV) electricity distribution and earth connection and how their evolution may have critically influenced the prevalence of the disturbing low frequency noise phenomenon (LFN) known as the Hum, or  Forty-five years on and do are we any closer to the real cause of the Hum?  by Dr Chris Barnes, Bangor Scientific and Educational Consultants, Bangor, Wales, UK e-mail manager@bsec-wales.co.uk     First released without reference list in interest of enlightening the public and scientific community alike : November 15th 2015.   



This present study has been prompted by considering previously recorded striking differences in the ground current spectra harmonics and inter-harmonics  at the author’s Bangor address have previously been highlighted at time when the Hum is perceived and times when it is not, see http://www.drchrisbarnes.co.uk/groundcurrent.html.

The history and suggested causes of the LFN phenomenon referred to as the Hum are briefly discussed.   Evidence that the       Hum is associated with power systems, is re-iterated.  Infrastructure changes  that took place in Britain at about the time when the Hum was first extensively heard are listed.  Types of earth grounding systems are reviewed.  They strongly influence ground current and harmonic behaviour. Earthing systems and the development of world HUM are more comprehensively discussed.  Mechanisms of Hum transduction and perception are briefly reviewed.  It has been shown by considering entries in the world hum database that the places in the world which experience most Hum are those with most TN ( TN-C-S) or PME earthing or grounding.  Moreover in areas  which have historically switched from TT –PME,  the temporal evolution of the Hum has followed EXACTLY the temporal evolution of the change in earthing system type.  The situation is accentuated when bonded metallic water and gas pipes are involved especially if they were used as the old TT CONSUMER earth connection. A small glimmer of hope may be that the Hum might be expected to reduce a little as gas and water distribution switches from metallic to plastic pipework thereby reducing circulating ground  current pathways.     Another strong implication   of power systems in the Hum has been found.




The enigmatic low frequency noise (LFN) phenomenon known as the Hum was first reported in Britain in the 1950’s and on a far more widespread basis in the 1970’s.   Most of the more well-known American Hum cases were reported in the 1990’s, with the exception of one reported case   in Oregon in  1976 [1]. 


Whether the Hum is one single phenomenon or a group of phenomena remains to be seen, but based on the author’s personal experience and    research and his study of UK reports and world-wide anecdotal reports and descriptions the latter seems most likely.   However, on balance power systems would appear to be responsible [2] for the vast majority of Hum cases  and this present paper will cement this conclusion.  


Descriptions  of the Hum phenomenon by hearers colloquially   referred to as ‘Hummers’ tend, generally,   to marry up with what is described as the effects of Infrasound [3] or Low Frequency Noise (LFN).   Vasudevan  and Gordon [4] have suggested that the Hum is difficult to trace because it is long distance noise propagated from distant factories.  The present author has shown that the perception of the Hum at his premises is always consistent with the presence of both infrasound and narrow band LFN below 300 Hz and he has proposed cochlear mechanisms for interaction and perception.  Such mechanisms are also discussed by Oud (2012) [5 ]  in the more general context of LFN.


Just occasionally       some Hum and             Hum- like LFN cases have been solved and put down to more local industrial noise emissions with related infrasound and LFN such as, for example, the Kokomo Hum and the case of heating systems described by Feldman and Pitten (2004)[6].  It must remembered however that many industrial motors, fans and compressors are in some way mains synchronous.


If the Hum were simply due to distant factory noise it is extremely difficult to say why it should have had a recent start date.  Also  there are  factories in many countries of the world wherein either the Hum has never ever been heard or is only just beginning to be perceived.


Thus there are those who have tried to explore infrastructure changes, particularly in Britain,   in search of a definite cause for the Hum.   In that respect, Fox ascribed the Hum as being due to motorways and High Pressure Gas Mains both new features of  Britain in the 1970’s [7]. 


Amateur Hum investigator John        Dawes  [1] showed a geographic distribution of the Hum correlating with the electricity power grid.  However, we should not, perhaps at least for the time being, lose sight of the fact that the Gas Grid uses many common corridors with the electricity grid,  see Markovic et al (2004) [8].    More recently the present author too, has found links with the Hum and energy infrastructure, particularly wind energy and hydropower employing Francis turbines, see Barnes 2013 [9].   There is now independent corroboration of Francis Turbine Hum, particularly Penstock Infrasound and Penstock Transformer Beat Frequencies given by Den Hartog (2013) in his book ‘Mechanical Vibrations’ [10].    


In order to fully explain all the observed properties of the Hum both at the level of personal experience and those reported anecdotally by others, one cannot but help reach the conclusion that the Hum is far more than just a noise.   Either there could be more than one type of Hum generation, transmission and  perception and/or Hum perception could potentially be augmented by the presence of fields other than acoustic ones. In this latter respect the author has noticed that the Hum intensity is related to alternating frequency magnetic components as well as to infrasonic and acoustic ones.    Moreover, he has shown that the Hum or rather Hum like effects in sensitive people can be synthesised in the laboratory using both acoustic and electromagnetic techniques. 


Baguley (2009) and again in (2013) has suggested the Hum is merely the product of over sensitive hearing and has piloted psycho-analytical techniques to reduce people’s anxiety [11].   The present author has previously asked the question, if over sensitivity is the case, why  then has it sudden reached more explosive proportions in the population at large.  Clearly there must be some environmental factor causing the sensitization or augmenting the Hum.  He went on to consider the advent of UHF TV and digital mobile communications technology as a possible candidate.   


Very recently indeed, the present author has re-visited the idea of seeking out further technological and infrastructure changes  that took place in Britain at about the time when the Hum was first extensively heard.   Such changes are summarised as and the first 5 bulleted points have been dealt with by the present author elsewhere:


·       Pumped storage ( renewable electricity)

·       First experimental wind turbines

·       UHF  all night TV

·       High Pressure Natural Gas Mains

·       Active Corrosion Protection of Gas Mains and the like

·       A lot less TT Electricity Earthing systems and more TNC(S) /PME earthing systems.



In addition to the differences in infrasound and acoustic spectra, striking differences in the ground current spectra harmonics and inter-harmonics  at the author’s Bangor address have previously been highlighted at time when the Hum is perceived and times when it is not, see http://www.drchrisbarnes.co.uk/groundcurrent.html [12].

Ground currents in the vicinity of properties vary enormously depending on the type of earthing   and/or  bonding that is employed. If metallic water and gas pipes are earth bonded some of the neutral current flows in them, see Simmons (2004) [13].  Indeed they often present a lower impedance than cables.  Some  types of earthing system are more prone to harmonics than others.   Of crucial importance to the present argument, abnormal ground currents and larger than average EMF Milligauss  values were noticed at some of the sites of the original Taos Hum. Dellabelle (2002) has discussed earthing systems in great detail, particularly with regard to use with digital communications.   He concludes that ‘TT’ is by far and above the best system.

A comparison of the different types of available earthing system round the world and their properties is given I the table below:







Earth fault loop impedance






RCD preferred?






Need earth electrode at site?






PE conductor cost






Risk of broken neutral








Less Safe


Least Safe


Electromagnetic interference






Safety risks

High loop impedance (step voltages)

Double fault, overvoltage

Broken neutral

Broken neutral

Broken neutral


Safe and reliable

Continuity of operation, cost



Safety and cost



To understand the table the terminology       needs to be understood.          Where:            

    "T" — Direct connection of a point with earth (Latin: terra)


    "I" — No point is connected with earth (isolation), except perhaps via a high impedance.


The second letter indicates the connection between earth and the electrical device being supplied:


    "T" — Direct connection of a point with earth


    "N" — Direct connection to neutral at the origin of installation, which is connected to the earth     


PE = PROTECTIVE EARTH     PEN= combined protective earth neutral




            IT  system                                                                TT system






TN-S:                                                          TN-C:                                                                                     TNC-S


TN-S: separate protective earth (PE) and neutral (N) conductors from transformer to consuming device, which are not connected together at any point after the building distribution point.

TN-C: combined PE and N conductor all the way from the transformer to the consuming device.          



Part of the system uses a combined PEN conductor, which is at some point split up into separate PE and N lines. The combined PEN conductor typically occurs between the substation and the entry point into the building, and separated in the service head. In the UK, this system is also known as protective multiple earthing (PME), because of the practice of connecting the combined neutral-and-earth conductor to real earth at many locations, to reduce the risk of electric shock in the event of a broken PEN conductor - with a similar system in Australia and New Zealand being designated as multiple earthed neutral (MEN).


Earthing systems and the development of world HUM

In Britain up to the 1950’s all supplies were TT and some were unearthed. Further,  up to the   1970’s most mains earthing installations were either TT or TN-S with TT being popular in overhead supplies and TN-S with lead sheathed cables in underground supplies. Since the 1970’s some TN-C-S  or PME is used in the UK.  EONS’ policy since 2007 is to only offer almost exclusively PME to residential customers. The latter is far worse for harmonics and phase imbalance induced currents, see for example,    http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=53310   [14].   Additional problems occur because of bonding, so if current also flows in say water and gas pipes, a ground loop can occur. Electromagnetic disturbances are known to occur on any metalwork bonded to the PE of a PME system.

For buried infrastructure cables and pipes acoustic noise can occur. This has been shown independently of the present author’s work.   For buried infrastructure in the neighbourhood of active CP there is the prospect of amplification of such noise and vibration.  The more harmonics and phase imbalance i.e. with PME, the more noise will occur.  


In the USA most wiring had TT and no earths up until as late as 1970.   Another reference states this was the case in some US areas until the mid-1990’s! Presently in the United States National Electrical Code and Canadian Electrical Code the feed from the distribution transformer uses a combined neutral and grounding conductor, but within the structure separate neutral and protective earth conductors are used (TN-C-S). The neutral must be connected to earth only on the supply side of the customer's disconnecting switch.  With the advent of this grounding system, the Hum began.


In Australia, New Zealand and Israel the TN-C-S system is in use; however, the wiring rules currently state that, in addition, each customer must provide a separate connection to earth via both a water pipe bond (if metallic water pipes enter the consumer's premises) and a dedicated earth electrode. In Australia and New Zealand this is called the Multiple Earthed Neutral Link or MEN Link. This MEN Link is removable for installation testing purposes, but is connected during use by either a locking system (locknuts for instance) or two or more screws. In the MEN system, the integrity of the Neutral is paramount. In Australia, new installations must also bond the foundation concrete re-enforcing under wet areas to the earth conductor (AS3000), typically increasing the size of the earthing, and provides an equipotential plane in areas such as bathrooms. In older installations, it is not uncommon to find only the water pipe bond, and it is allowed to remain as such, but the additional earth electrode must be installed if any upgrade work is done. The protective earth and neutral conductors are combined until the consumer's neutral link (located on the customer's side of the electricity meter's neutral connection) - beyond this point, the protective earth and neutral conductors are separate.  The situation is similar in Argentina.   All four countries have the Hum. 


Older homes in Norway uses the IT system while newer homes use TN-C-S.  There is some Hum in Norway but not a huge amount as adjudged by visits to the world Hum database.


Japan is governed by PSE law, and uses TT earthing in most installations.  It also uses underground GIS substations and until recently had no Hum at all. Despite being one of the most seismically active parts of the world.


In Denmark the high voltage regulation (Stærkstrømsbekendtgørelsen) and Malaysia the Electricity Ordinance 1994 states that all consumers must use TT earthling, though in rare cases TN-C-S may be allowed (used in the same manner as in the United States). Rules are different when it comes to larger companies.  Both countries have had a few cases of Hum since they have had some TN-C-S earthing. 


South Africa has TN-C-S (PME)  and has the Hum.


All three earthing systems are used in China to some extent and China now has the Hum.


France has used TN since 1973 and has the Hum.


Rural Ireland had TT originally but now have PME and have the Hum.


The rest of Europe started historically with the TT system but now have PME and most parts of Europe now have the Hum. 

The  TT system however remains the most widely used grounding system in the world, a product of its versatility and reasonable cost of protection devices. All the African countries which don’t experience the Hum use the TT system.  The literature is not explicit but following Lacroix and Calvus  and applying a process of elimination it would seem that Russia has mainly the TT system and until recently has no Hum at all.


Summary : TT = NO Hum   TN-C-S (PME) = Maximum Hum.  ALL3 = Some Hum


The above geospatial evidence cannot be disputed.  Areas on the planet which have TT  earthing alone have no Hum.  Areas which have PME earthing ALL have the Hum.



Bonding and the Hum    

Bonding is the principal of connection all metalwork in a premises together so that it is equipotential and the bonding point is then taken to an earth connection. 

Strictly speaking with the IT earthing system there should be no earth at the consumers premises only at the substation.  With the TT earth system metalwork would be bonded and earthed at the consumer’s  home with no connection to neutral. Ideally proper buried earth electrodes or grids should be used but in a lot of countries and rural locations metal water and gas pipes have finished up being the only earth connection. 

The complication occurs when electricity suppliers decide to update to using tied earth neutral systems of whatever kind.  Effectively, if the old bonded earth connection  and the new earth connection remain then there is more than one pathway for fault current, return current and harmonic induced ground current to flow.  The situation is worst for PME where harmonics and noise from neighbouring consumers and supplies can be  felt to some extent by all consumers on the phase circuit and to some extent there will be cross-Talking from the other two phases as well.  If the infrastructure is close together there will even be the possibility to feel some noise injection from the MV and HV networks as well.  Additional circulating currents in the ground and additional seismo-acoustic vibrations in the ground offer additional possibility for acoustic amplification in the presence of DC CP fields and the like, see Barnes (2015) [15].   In addition to these local ground current disturbances, since power grids world-wide have the potential even to couple with space weather ground current disturbances can even be induced from huge distances away under certain conditions of the Interplanetary  Magnetic Field giving also the possibility of mixing of preternatural frequency pulsations with those of the power system.    For example signals from the UK power grid have been detected in the USA.  82 Hz submarine transmission is detected world-wide.  The present author has received European pulsadis signals on a ground loop antenna etc. etc.         Radio frequency fields too  are known to be very good at entering PME circuits and may be demodulated as a wall voltage. Such was noted by EMSCITEK in the Kokomo Hum Study.


Relevance to Hum mechanisms 

In a nutshell one could almost read  ‘harmonic’ for Hum.  For when harmonics are present there will often be coincident other types of power disturbance such as sub-harmonic, inter-harmonic, wind –turbine flicker and inter and intra-area oscillation and all or any of the above types of signal. All are heavily accentuated in countries which use PME earthing especially if metallic water and gas mains are also earth bonded.    All these frequencies have the opportunity to form coherent and quasi-coherent acoustic, seismic, airborne and structure borne vibrations as well as  electromagnetic disturbances in buildings and residences.         As discussed elsewhere there are multiple possible modes of transmission   of the Hum and more than one possible mode of human perception.    Switching off the power to a house will make no difference whatsoever to these signals.


Transmission into buildings.

Seismo-acoustic signals of the Hum can enter building as a surface Rayleigh wave and room resonant amplification can follow.  One strange feature of the Hum is that it sometimes seems as though it pervades all the air in a building.  A way in which this can happen is if the inner walls of the building actually (structurally) radiate  both acoustic and electromagnetic signals. The author has discussed this elsewhere but basically brick is a  piezoelectric material and the bases of all the walls can never be in exact equipotential  with the house earth connection. There will always be field gradients.      There will also be weak time varying magnetic fields, worse with PME.    More distant components of the Hum  either direct from the edge of space or from wind turbines could be airborne and enter via windows, chimney excitation  or wave –wave interaction processes.  Other more distant components of the Hum from seismic sources such as hydro turbines could enter as ground borne vibrations.  Nothing here rules out a Hum component which is not generated by the power grid, e.g. gas or water mains noise  or  EVEN demodulated RF   but we cannot escape the inevitable conclusion that world- over ,   countries with  100%  TT and 0%  renewable power certainly seems 100% to equate with Hum free.      


In its simplest sense the Hum can be an LFN phenomenon, some components of which are not of sufficient amplitude to record, see for example Oud [5].  However,  there is sufficient evidence to suggest that for some individuals magnetic perception and even gravitational perception may feature as either direct methods of perception or as augmenters   of the Hum.        Such evidence exists at all levels;  theoretical, anecdotal and personal.  There is also independent experimental evidence of a moving electromagnetic field evoking involuntary movement in human subjects.  



It has been shown by considering entries in the world hum database that the places in the world which experience most Hum are those with most TN ( TN-C-S) or PME earthing or grounding.  Moreover in areas  which have historically switched from TT –PME , the temporal evolution of the Hum has followed EXACTLY the temporal evolution of the change in earthing system type.  The situation is accentuated when bonded metallic water and gas pipes are involved especially if they were used as the old TT CONSUMER earth connection. A small glimmer of hope may be that the Hum might be expected to reduce a little as gas and water distribution switches from metallic to plastic pipework thereby reducing circulating ground  current pathways.     Quite categorically this is yet another strong and virtually incontrovertible indicator of the implication of power systems in the Hum.



The author wishes to acknowledge his wife Gwyneth for valuable discussions  on the Hum and together with his son Dwain   for both their contributions as experimental subjects.




1.     http://www.johndawes.pwp.blueyonder.co.uk/history.htm

2.     http://www.drchrisbarnes.co.uk/HUMGRIDEFO.htm

3.     http://multi-science.atypon.com/doi/abs/10.1260/147547303322773381

4.     R.N. Vasudevan, Colin G. Gordon, Applied Acoustics, 10(1),

5.     http://home.kpn.nl/oud/publications/OudM_ProcGTLGG2012.pdf

6.      http://www.noiseandhealth.org/article.asp?issn=1463-1741;year=2004;volume=7;issue=25;spage=23;epage=28;aulast=Feldmann

7.      Fox B. (1989) Low frequency ‘Hum’ May Permeate the Environment, New Scientist, December 9th , 1989, p27.

8.     http://www.elec.uow.edu.au/apqrc/content/papers/AUPEC/AUPEC04_6.pdf

9.      http://www.drchrisbarnes.co.uk/Italy.htm

10.  https://books.google.co.uk/books?id=IlN8CgAAQBAJ&pg=PT17&lpg=PT17&dq=Hum++Francis+turbine.&source=bl&ots=zmAlEP6ta_&sig=PQ2hYpVM-CWEelJvsZsigiy64Cw&hl=en&sa=X&ved=0ahUKEwjE-63ti4fKAhVCPxoKHTiuA0cQ6AEILTAC#v=onepage&q=Hum%20%20Francis%20turbine.&f=false

11.   http://latestnewsvideos.org/sciencetech/article-1184592/Have-heard-The-Hum-The-throbbing-noise-just-wont-away.html    

12.  http://www.drchrisbarnes.co.uk/groundcurrent.html  

13.  J. Philip Simmons Electrical Grounding and Bonding Cengage Learning, 1 Dec 2004 - Technology & Engineering - 292 pages

14.  http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=53310   

15.  http://drchrisbarnes.co.uk/CP1.htm