the following definitions are to be used to interpret the meaning of the terms discussed in the description and recited in the claims . as used herein , the article “ a ” indicates one as well as more than one and does not necessarily limit its referent noun to the singular . as used herein , the terms “ about ” and “ at or about ” mean that the amount or value in question may be the value designated or some other value that is approximately or about the same . the phrase is intended to convey that similar values promote equivalent results or effects according to the invention . as used herein , the term “ melting point ” in reference to a polyamide refers to the melting point of the pure resin as determined with differential scanning calorimetry ( dsc ) at a scan rate of 10 ° c ./ min in the first heating scan , wherein the melting point is taken at the maximum of the endothermic peak . in customary measurements of melting behavior of blends of polymers , more than one heating scans may be performed on a single specimen , and the second and / or later scans may show a different melting behavior from the first scan . this different melting behavior may be observed as a shift in temperature of the maximum of the endothermic peak and / or as a broadening of the melting peak with possibly more than one peaks , which may be an effect of possible transamidation in the case of more than one polyamides . however , when selecting polyamides in the scope of the current invention , always the peak of the melting endotherm of the first heating scan of the single polyamide is used . as used herein , a scan rate is an increase of temperature per unit time . sufficient energy must be supplied to maintain a constant scan rate of 10 ° c ./ min until a temperature of at least 30 ° c . and preferably at least 50 ° c . above the melting point is reached . polyamides are condensation products of one or more dicarboxylic acids and one or more diamines , and / or one or more aminocarboxylic acids , and / or ring - opening polymerization products of one or more cyclic lactams . polyamides may be fully aliphatic or semi - aromatic and are described hereafter . the term “ semi - aromatic ” describes polyamides that comprise at least some monomers containing aromatic groups , in comparison with “ fully aliphatic ” polyamide which describes polyamides comprising aliphatic carboxylic acid monomer ( s ) and aliphatic diamine monomer ( s ). the one or more semi - aromatic polyamides ( a ) may be derived from one or more aliphatic carboxylic acid components and aromatic diamine components such as for example m - xylylenediamine and p - xylylenediamine , it may be derived from one or more aromatic carboxylic acid components , such as terephthalic acid , and one or more aliphatic diamine components , it may be derived from mixtures of aromatic and aliphatic dicarboxylic acid components and mixtures of aromatic and aliphatic diamine components , it may be derived from mixtures of aromatic and aliphatic carboxylic acids and aliphatic diamines or aromatic diamines , it may be derived from aromatic or aliphatic carboxylic acids with mixtures of aliphatic and aromatic diamines . preferably , the one or more semi - aromatic polyamides ( a ) are formed from one or more aromatic carboxylic acid components and one or more aliphatic diamine components . the one or more aromatic carboxylic acids can be , for example , terephthalic acid or mixtures of terephthalic acid and one or more other carboxylic acids , such isophthalic acid , substituted phthalic acid such as for example 2 - methylterephthalic acid and unsubstituted or substituted isomers of naphthalenedicarboxylic acid , wherein the carboxylic acid component contains at least 55 mole -% of terephthalic acid ( the mole -% being based on the carboxylic acid mixture ). preferably , the one or more aromatic carboxylic acids are selected from terephthalic acid , isophthalic acid and mixtures thereof and more preferably , the one or more carboxylic acids are mixtures of terephthalic acid and isophthalic acid , wherein the mixture contains at least 55 mole -% of terephthalic acid . more preferably , the one or more carboxylic acids is 100 % terephthalic acid . furthermore , the one or more carboxylic acids can be mixed with one or more aliphatic carboxylic acids , like adipic acid ; pimelic acid ; suberic acid ; azelaic acid ; sebacic acid and dodecanedioic acid , adipic acid being preferred . more preferably the mixture of terephthalic acid and adipic acid comprised in the one or more carboxylic acids mixtures of the one or more semi - aromatic polyamide ( a ) contains at least 55 mole -% of terephthalic acid . the one or more semi - aromatic polyamides ( a ) described herein comprises one or more aliphatic diamines that can be chosen among diamines having four or more carbon atoms , including , but not limited to tetramethylene diamine , hexamethylene diamine , octamethylene diamine , decamethylene diamine , 2 - methylpentamethylene diamine , 2 - ethyltetramethylene diamine , 2 - methyloctamethylene diamine ; trimethylhexamethylene diamine , bis ( p - aminocyclohexyl ) methane ; and / or mixtures thereof . preferably , the one or more diamines of the one or more semi - aromatic polyamides ( a ) described herein are selected from hexamethylene diamine , 2 - methyl pentamethylene diamine and mixtures thereof , and more preferably the one or more diamines of the one or more semi - aromatic polyamides ( a ) are selected from hexamethylene diamine and mixtures of hexamethylene diamine and 2 - methyl pentamethylene diamine wherein the mixture contains at least 50 mole -% of hexamethylene diamine ( the mole -% being based on the diamines mixture ). examples of semi - aromatic polyamides ( a ) useful in the flame retardant composition described herein are commercially available under the trademark zytel ® htn from e . i . du pont de nemours and company , wilmington , del . preferred semi - aromatic polyamides ( a ) have a melting point of at least 280 ° c ., and comprise a semiaromatic polyamide selected from the group consisting of poly ( ε - caprolactam / tetramethylene terephthalamide ) ( pa6 / 4t ), poly ( ε - caprolactam / hexamethylene terephthalamide ) ( pa6 / 6t ), poly ( ε - caprolactam / decamethylene terephthalamide ) ( pa6 / 10t ), poly ( ε - caprolactam / dodecamethylene terephthalamide ) ( pa6 / 12t ), poly ( hexamethylene decanediamide / hexamethylene terephthalamide ) ( pa610 / 6t ), poly ( hexamethylene dodecanediamide / hexamethylene terephthalamide ) ( pa612 / 6t ), poly ( hexamethylene tetradecanediamide / hexamethylene terephthalamide } ( pa614 / 6t ), poly ( ε - caprolactam / hexamethylene isophthalamide / hexamethylene terephthalamide ) ( pa6 / 6i / 6t ), poly ( 2 - methylpentamethylene hexanediamide / hexamethylene hexanediamide / hexamethylene terephthamide ) ( pa d6 / 66 / 6t ), poly ( hexamethylene terephthamide / 2 - methylpentamethylene terephthamide ) ( pa 6t / xt ), poly ( hexamethylene hexanediamide / hexamethylene terephthamide ( pa66 / 6t ), poly ( hexamethylene terephthamide / hexamethylene isophthamide ( pa6t / 6i ), poly ( hexamethylene hexanediamide / hexamethylene terephthamide / hexamethylene isophthamide ( pa66 / 6t / 6i ), poly ( decamethylene decanediamide / decamethylene terephthalamide ) ( pa1010 / 10t ) poly ( decamethylene decanediamide / dodecamethylene decanediamnide / decamethylene terephthalamide / dodecamethylene terephthalamide ( pa1010 / 1210 / 10t / 12t ), poly ( 11 - aminoundecanamide / tetramethylene terephthalamide ) ( pa11 / 4t ), poly ( 11 - aminoundecanamide / hexamethylene terephthalamide ) ( pa11 / 6t ), poly ( 11 - aminoundecanamide / decamethylene terephthalamide ) ( pa11 / 10t ), poly ( 11 - aminoundecanamide / dodecamethylene terephthalamide ) ( pa11 / 12t ), poly ( 12 - aminododecanamide / tetramethylene terephthalamide ) ( pa12 / 4t ), poly ( 12 - aminododecanamide / hexamethylene terephthalamide ) ( pa12 / 6t ), poly ( 12 - aminododecanamide / decamethylene terephthalamide ) ( pa12 / 10t ), and poly ( dodecamethylene dodecanediamide / dodecamethylene dodecanediamide / dodecamethylene terephthalamide )) ( pa1212 / 12t ), and their copolymers and combinations . particularly preferred semi - aromatic polyamides are selected from the group consisting of pa66 / 6t , pa6t / xt , pa6t / 6i , and their combinations and copolymers . the flame retardant polymer composition of the present invention may also be a blend of one or more semi - aromatic polyamides described above with one or more homopolymers , copolymers , terpolymers , or higher polymers that are derived fully aliphatic polyamides . examples of aliphatic polyamide homopolymers , copolymers , or terpolymers that may be blended with the semi - aromatic polyamides of the present invention include polyamide 6 , polyamide 66 , polyamide 610 , polyamide 612 , polyamide 46 , polyamide 66 / 6 copolymers , polyamide 66 / 68 copolymers , polyamide 66 / 610 copolymers , polyamide 66 / 612 copolymers , polyamide 66 / 10 copolymers , polyamide 66 / 12 copolymers , polyamide 6 / 68 copolymers , polyamide 6 / 610 copolymers , polyamide 6 / 612 copolymers , polyamide 6 / 10 copolymers , polyamide 6 / 12 copolymers , polyamide 6 / 66 / 610 terpolymers , polyamide 6 / 66 / 69 terpolymers , polyamide 6 / 66 / 11 terpolymers , polyamide 6 / 66 / 12 terpolymers , polyamide 6 / 610 / 11 terpolymers , polyamide 6 / 610 / 12 terpolymers , and polyamide 6 / 66 / pacm where palm refers to his - p -( aminocyclohexyl ) methane )] terpolymers . flame retardance in the flame retardant polyamide compositions described herein is imparted by flame retardant mixtures also referred herein as flame retardant compositions . these flame retardant mixtures ( b ) comprise a flame retardant b1 ) which is a phosphinate of the formula ( i ) ( i . e . a monophosphinate ) and / or a diphosphinate of the formula ( ii and / or polymers of ( i ) and / or ( ii ), wherein r 1 and r 2 are identical or different and are hydrogen , linear or branched c 1 - c 6 alkyl groups , and / or aryl groups ; r 3 is a linear or branched c 1 - c 10 - alkylene group , a c 6 - c 10 - arylene group , an alkylarylene group or arylalkylene group ; m is calcium , magnesium , aluminum , and / or zinc ; m is 2 to 3 ; n is 1 or 3 ; and x is 1 or 2 . r 1 and r 2 may be identical or different and are preferably hydrogen , methyl , ethyl , n - propyl , isopropyl , n - butyl , tent - butyl , n - pentyl and / or phenyl . r 3 is preferably methylene , ethylene , n - propylene , isopropylene , n - butylene , tent - butylene , n - pentylene , n - octylene , n - dodecylene , or phenylene or naphthylene , or methylphenylene , ethylphenylene , tert - butylphenylene , methylnaphthylene , ethylnaphthylene or tert - butylnaphthylene , or phenylmethylene , phenylethylene , phenylpropylene or phenylbutylene . m is preferably aluminum or zinc . by polymers of the compounds of formulas ( i ) and ( ii is meant species containing oligomers or condensation products of the phosphinate and diphosphinate anion moieties . preferred phosphinates are metal salts of organic phosphinates , such as metal salts of methylethylphosphinates and diethylphosphinates . more preferred are aluminum methylethylphosphinate , aluminum diethylphosphinate , zinc methylethylphosphinate , and zinc diethylphosphinate . more preferably , the flame retardant is aluminum phosphinate , magnesium phosphinate , calcium phosphinates and / or zinc s phosphinate and still more preferably , the flame retardant is aluminum phosphinate , aluminum diethyl phosphinate and / or zinc diethyl phosphinate . the flame retardant b1 ) is usually in the form of particles which may have any particle size distribution , as commonly understood and used by lo those having skill in the field , but preferably the phosphinate and / or diphosphinates that comprise component b1 ) have particle sizes ( d50 value ) of less than or equal to 100 microns and more preferably less than or equal to 50 microns . the d50 value corresponds to a particle size below which 50 weight percent of the particles lie , wherein the particle size distribution is measured by the technique of laser diffraction from a suspension of particles in a solvent using a particle size analyzer , mastersizer 2000 from malvern . this test method meets the requirements set forth in iso 13320 . preferably , the flame retardant mixtures ( b ) comprise a flame retardant b1 ) in an amount from at or about 10 to at or about 30 weight percent , more preferably from at or about 15 to at or about 25 weight percent , and even more preferably from at or about 18 to at or about 20 weight percent , the weight percentage being based on the total weight of the flame retardant polyamide composition . the flame retardant mixtures ( b ) described herein comprise a phosphate ester flame retardant b2 ) of formula ( iii ). wherein r4 and r5 each independently represent a hydrogen atom or a methyl group and n represents a number of 1 to 5 . the phosphate ester flame retardant b2 ) may be a mixture of the monomers or oligomers of compound of formula ( iii i . e . a mixture of compounds wherein n is equal to 1 and n is equal to 2 , 3 , 4 or 5 . phosphate ester flame retardants of the present invention may be obtained , for instance , according to the processes described in u . s . patent application us 2011 / 0084242 . preferred phosphate ester flame retardant b2 ) are the ones with cas number 1003300 - 73 - 9 available from adeka palmarole . preferably , the flame retardant mixtures ( b ) comprise a phosphate ester flame retardant b2 ) in an amount from at or about 0 . 5 to at or about 3 weight percent , more preferably from at or about 0 . 75 to at or about 1 . 5 weight percent , the weight percentage being based on the total weight of the flame retardant polyamide composition . the flame retardant compositions of the present invention may further contain other additives that can be selected from the group consisting of stabilizers , processing agents , metal deactivators , antioxidants , uv stabilizers , heat stabilizers , flame retardant synergists , dyes and / or pigments and other additives in addition to the components mentioned previously . flame retardant synergists may also be optionally included in the composition in conventional amounts and as understood by those having skill in the field . examples include silicone , metal oxides such as silica , boehmnite , aluminum oxide , iron oxide , titanium oxide , manganese oxide , magnesium oxide , zirconium oxide , zinc oxide , molybdenum oxide , cobalt oxide , bismuth oxide , chromium oxide , tin oxide , antimony oxide , nickel oxide , copper oxide and tungsten oxide , metal powder such as aluminum , iron , titanium , manganese , zinc , molybdenum , cobalt , bismuth , chromium , tin , antimony , nickel , copper and tungsten , and metal salts such as zinc s borate , zinc metaborate , barium metaborate , zinc carbonate , zinc stannate , magnesium carbonate , calcium carbonate , and barium carbonate . preferred synergists are boehmite ( aluminum hydroxide oxide ( alo ( oh ))), aluminum oxide , zinc borate , zinc stannate and mixtures thereof . synergists will preferably be present in up to about 10 weight percent or more preferably in about 0 . 5 to about 8 weight percent , or yet more preferably in about 1 to about 6 weight percent , based on the total weight of the flame retardant polyamide composition . the flame retardant polyamide compositions of the present invention are melt - blended and can be manufactured by any known manufacturing methods . the component materials may be mixed to homogeneity using a melt - mixer such as a single or twin - screw extruder , blender , kneader , banbury mixer , etc . to give a resin composition . or , part of the materials may be mixed in a melt - mixer , and the rest of the materials may then be added and further melt - mixed until homogeneous . the articles of the present invention may be formed from the flame retardant polyamide compositions of the invention by any known means such as injection molding , blow molding , extrusion , or thermoforming . examples of articles that may be formed from the flame retardant polyamide compositions of the present invention are housings , electrical connectors and connector housings and cases , breaker housings , terminal blocks and contactor housings . the invention is further illustrated by certain embodiments in the examples below which provide greater detail for the compositions , uses and processes described herein . the following materials were used to prepare the flame retardant polyamide compositions described herein and the compositions of the comparative examples . as required for the manufacturing process and well - known to those skilled in the art , the polyamide contained up to 2 weight percent of heat stabilizers , uv stabilzers , antioxidants and lubricants . the components were dry blended and then compounded with a screw speed of 300 rpm using a twin - screw extruder . the barrel temperatures were about 320 ° c . upon exiting the extruder , the molten polymer was quenched in a water bath and pelletized . test specimen have been prepared using an injection moulding machine ( billion h470 - 150t select dixit ii diameter 32 mm , ratio l / d 19 ) at a melt temperature of 325 ° c . and a mold temperature of 100 ° c . except for flammability , all properties have been measured on dry as moulded ( dam ) samples . tensile properties ( tensile modulus , stress at break and elongation at break ) have been measured using iso 527 - 2 / 1a / 50 values in the examples are average values of 10 specimens . notched charpy was measured using iso 179 - 1 / 1 ea and unnotched charpy was measure using iso 179 - 1 / 1 eu . values in the examples are average values of 10 specimens . comparative tracking index ( cti ) was measured using iec 60112 on 4 mm iso bars . values in the examples are average values of 5 specimens . flammability testing was done according to ul - 94 ( 20 mm vertical burning test ) using 0 . 4 mm or 0 . 8 mm thick test pieces , which are then conditioned for either 48 hours at 23 ° c . and 50 % relative humidity or 168 hours at 70 ° c . values in the examples are average values of 10 specimens . in table 1 , comparative examples c1 , c2 , c3 show that impact modifiers are efficient to improve elongation at break of unreinforced and flame retardant composition of pa6t / 66 but reduce its flammability performances . it shows that it is not possible to achieve 5 % elongation at break while maintaining ul - v0 flammability performances even at 0 . 8 mm . in table 2 , comparative examples c4 , c5 and c6 show that increasing the flame retardant level in unreinforced and flame retardant composition of pa6t / 66 containing impact modifier does not allow to achieve ul - v0 but reduces the elongation at break . in table 3 , examples e1 , e2 and e3 show that the addition of phosphate ester increases elongation at break of unreinforced and flame retardant composition of pa6t / xt containing impact modifier . in table 4 , examples e4 , e5 and e6 and comparative examples c7 and c8 show that the addition of phosphate ester increases elongation at break of unreinforced and flame retardant composition of pa6t / 66 . the increase of elongation at break varies with the amount of phosphate ester and is higher for example e4 which contains the highest level of s phosphate ester . example e4 and comparative examples c7 and c8 show that the addition of phosphate ester in unreinforced and flame retardant composition of pa6t / 66 improves the flammability performances of the composition and allows to achieve ul - v0 at 0 . 4 mm and 0 . 8 mm without use of any flame retardant synergist ( e . g . boehmite ).